 Section 42 of Gray's Anatomy, Part 4 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by David Lawrence. Anatomy of the Human Body, Part 4 by Henry Gray. Sacral and Coxigial Nerves, Part 2 The common peroneal nerve, Nervous Peroneus Communus, External Papetial Nerve, Paroneal Nerve About one half the size of the tibial is derived from the dorsal branches of the fourth and fifth lumbar and the first and second sacral nerve. It descends obliquely along the lateral side of the papetial fossa to the head of the fibula, close to the medial margin of the biceps femoris muscle. It lies between the tendon of the biceps femoris and lateral head of the gastrocnemius muscle, winds around the neck of the fibula, between the peronatus longus and the bone, and divides between the muscle into the superficial and deep peroneal nerves. Previous to its division, it gives off articular and lateral serocutaneous nerves. The articular branches, rami articularis, are three in number. Two of these accompany the superior and inferior lateral genicular arteries to the knee. The upper one occasionally arises from the trunk of the sciatic nerve. The third, recurrent, articular nerve is given off at the point of division of the common peroneal nerve. It ascends with the anterior recurrent tibial artery through the tibialis anterior to the front of the knee. The lateral serocutaneous nerve, nervous cutaneous serae lateralis, lateral cutaneous branch supplies the skin on the posterior and lateral surfaces of the leg. One branch, the peroneal anastomonic, nervous communicans fibularis, arises near the head of the fibula, crosses the lateral head of the gastrocnemius to the middle of the leg, and joins with the medial serocutaneous to form the seronal nerve. The peroneal anastomonic is occasionally continued down as a separate branch as far as the heel. The deep peroneal nerve, nervous peroneus profundus anterior tibial nerve begins at the bifurcation of the common peroneal nerve between the fibula and the upper part of the peroneus longus, passes obliquely forward beneath the extensor digitorum longus to the front of the interosseous membrane and comes into relation with the anterior tibula artery above the middle of the leg. It then descends with the artery to the front of the ankle joint, where it divides into a lateral and medial terminal branch. It lies at first at the lateral side of the anterior tibial artery, then in front of it and again on its lateral side at the ankle joint. In the leg the deep peroneal nerve supplies muscular branches to the tibialis anterior, extensor digitorum longus, peroneus tertius and extensor helusis propius and an articular branch to the ankle joint. The lateral terminal branch, external or tarsal branch, passes across the tarsus beneath the extensor digitorum brevis and having become enlarged like the dorsal interosseous nerve at the wrist supplies the extensor digitorum brevis. From the enlargement three minute interosseous branches are given off, which supply the tarsal joints and the metatarsal phalangeal joints of the second, third and fourth toes. The first of these sends a filament to the second interosseous dorsalis muscle. The medial terminal branch, internal branch, accompanies the dorsalis pedis artery along the dorsum of the foot and at the first interosseous space divides into two dorsal digital nerves, nervi digitalis dorsalis helusis lateralis and digiti secundi medialis, which supply the adjacent sides of the great and second toes, communicating with the medial dorsal cutaneous branch of the superficial peroneal nerve. Before it divides, it gives off to the first space an interosseous branch, which supplies the metatarsal phalangeal joint of the great toe and sends the filament to the first interosseous dorsalis muscle. The superficial peroneal nerve, nervous peroneus superficialis musculos cutaneous nerve supplies the pirani longus and brevis and the skin over the greater part of the dorsum of the foot. It passes forward between the pironi and the extensor digitorum longus, pierces the deep fascia at the lower third of the leg and divides into a medial and an intermediate dorsal cutaneous nerve. In its course between the muscles, the nerve gives off muscular branches to the pironi longus and brevis and cutaneous filaments to the integument of the lower part of the leg. The medial dorsal cutaneous nerve, nervous cutaneous dorsalis medialis, internal dorsal cutaneous branch passes in front of the ankle joint and divides into two dorsal digital branches, one of which supplies the medial side of the great toe, the other the adjacent side of the second and third toes. It also supplies the integument of the medial side of the foot and ankle and communicates with the saphenous nerve and with the deep peroneal nerve. The intermediate dorsal cutaneous nerve, nervous cutaneous dorsalis intermedius, external dorsal cutaneous branch. The smaller passes along the lateral part of the dorsum of the foot and divides into the dorsal digital branches, which supply the contiguous sides of the third and fourth and of the fourth and fifth toes. It also supplies the skin of the lateral side of the foot and ankle and communicates with the serral nerve. The branches of the superficial peroneal nerve supply the skin of the dorsal surfaces of all the toes except the lateral side of the little toe and the adjoining sides of the great and second toes. The former being supplied by the lateral dorsal cutaneous nerve from the serral nerve and the latter by the medial branch of the deep peroneal nerve. Frequently some of the lateral branches of the superficial peroneal are absent and their places are then taken by branches of the serral nerve. The pudental plexus plexus pudentus. The pudental plexus is not sharply marked off from the sacral plexus and as a consequence some of the branches which spring from it may arise in conjunction with those of the sacral plexus. It lies on the posterior wall of the pelvis and is usually formed by branches from the anterior divisions of the second and third sacral nerves. The whole of the anterior divisions of the fourth and fifth sacral nerves and the coxigial nerve, it gives off the following branches perforating cutaneous, second and third sacral, pudental, second, third and fourth sacral, biscaryl, third and fourth sacral, muscular, fourth sacral, anocoxigial, fourth and fifth sacral and coxigial. The perforating cutaneous nerve, nervous clonium inferior medialis usually arises from the posterior surface of the second and third sacral nerves. It pierces the lower part of the sacro tuberous ligament and winding around the inferior border of the gluteus maximus supplies the skin covering the medial and lower parts of that muscle. The perforating cutaneous nerve may arise from the pudental or it may be absent. In the latter case its place may be taken by a branch from the posterior femoral cutaneous nerve or by a branch from the third and fourth or fourth and fifth sacral nerves. The pudental nerve, nervous pudentus internal pudic nerve derives its fibers from the ventral branches of the second, third and fourth sacral nerves. It passes between the piriformis and coxigial muscles and leaves the pelvis through the lower part of the greater sciatic foreman. It then crosses the spine of the ischium and re-enters the pelvis through the lesser sciatic foreman. It accompanies the internal pudental vessels upward and forward along the lateral wall of the itchiorectal fossa being contained in a sheath of the obturator fascia termed alcox canal and divides into two terminal branches vis the perineal nerve and the dorsal nerve of the penis or clitoris. Before its division, it gives off the inferior hemorrhoidal nerve. The inferior hemorrhoidal nerve, nervous hemorrhoidalis inferior, occasionally arises directly from the sacral plexus. It crosses the itchiorectal fossa with the inferior hemorrhoidal vessels toward the anal canal and the lower end of the rectum and is distributed to the sphincter, any externus and to the integument around the anus. Branches of this nerve communicate with the perineal branch of the posterior femoral cutaneous and with the posterior scrotal nerves at the forepart of the perineum. The perineal nerve, nervous perineae, the inferior and larger of the two terminal branches of the pudental, is situated below the internal pudental artery. It accompanies the perineal artery and divides into posterior scrotal or labial and muscular branches. The posterior scrotal or labial branches, nerve scrotalis or labialis, posterioris, superficial peroneal nerves are two in number, medial and lateral. They pierce the fascia of the urogenital diaphragm and run forward along the lateral part of the urethral triangle in company with the posterior scrotal branches of the perineal artery. They are distributed to the skin of the scrotum and communicate with the perineal branch of the posterior femoral cutaneous nerve. These nerves supply the labium magis in the female. The muscular branches are distributed to the transversus perineae superficialis, bobocavernous, itchiocavernosis and the constrictor urethra. A branch, the nerve to the bulb, given off from the nerve to the bobocavernosis, pierces this muscle and supplies the corpus cavernosum urethrae, ending in the mucous membrane of the urethra. The dorsal nerve of the penis, nervous dorsalis penis, is the deepest division of the pudental nerve. It accompanies the internal pudental artery along the ramus of the ischium. It then runs forward along the margin of the inferior ramus of the pubis between the superior and inferior layers of the fascia of the urogenital diaphragm. Piercing the inferior layer, it gives a branch to the corpus cavernosum penis and passes forward in company with the dorsal artery of the penis, between the layers of the suspensory ligament onto the dorsum of the penis and ends on the gland's penis. In the female, this nerve is very small and supplies the clitoris, nervous dorsalis clitoridus. The visceral branches arise from the third and fourth and sometimes from the second sacral nerves and are distributed to the bladder and rectum and in the female to the vagina. They communicate with the pelvic plexuses of the sympathetic. The muscular branches are derived from the fourth sacral and supply the levator ani, coxegius and sphincter ani externus. The branches of the levator ani and coxegius enter their pelvic surfaces, that to the sphincter ani externus, perineal branch, reaches the ischurectal fossa by piercing the coxegius or by passing between it and the levator ani. Cutaneous filaments from this branch supply the skin between the anus and the coxige. Anocoxigial Nerves Nervy Anocoxigia The fifth sacral nerve receives a communicating filament from the fourth and unites with a coxigial nerve to form the coxigial plexus. From this plexus, the anocoxigial nerves take origin. They consist of a few fine filaments which pierce the sacral tuberous ligament to supply the skin in the region of the coxis. Recording by David Lawrence in Brampton, Ontario, December 2009. Section number 43 of Graze Anatomy Part 4 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, visit LibriVox.org. Recording by ML Cohen, Anatomy the Human Body Part 4 by Henry Gray, The Sympathetic Nerves The sympathetic nervous system innervates all the smooth muscles and the various glands of the body and the striated muscles of the heart. The efferent sympathetic fibers which leave the central nervous system in connection with certain of the craniol and spinal nerves all end in sympathetic ganglia and are known as preganglionic fibers. From these ganglia, postganglionic fibers arise and conduct impulses to the different organs. In addition, afferent or sensory fibers connect many of these structures with the central nervous system. The peripheral portion of the sympathetic nervous system is characterized by the presence of numerous ganglia and complicated plexuses. These ganglia are connected with the central nervous system by three groups of sympathetic efferent that is the craniol, the thoracolumbar and the sacral. These outflows of sympathetic fibers are separated by intervals where no connections exist. The craniol and sacral sympathetics are often grouped together owing to the resemblance between the reactions produced by stimulating them and by the effects of certain drugs. Acetylcholine for example when injected intravenously in very small doses produces the same effect as the stimulation of the craniol or sacral sympathetics while the introduction of adrenaline produces the same effect as the stimulation of the thoracolumbar sympathetics. Much of our present knowledge of the sympathetic nervous system has been acquired through the application of various drugs especially nicotine which paralyzes connections or synapses between the preganglionic and postganglionic fibers of the sympathetic nerves. When it is injected into the general circulation all such synapses are paralyzed. When it is applied locally on the ganglion only the synapses occurring in that particular ganglion are paralyzed. Langley, who has contributed greatly to our knowledge adapt the determinology somewhat different from that used here and still different from that used by the pharmacologist. This has led to considerable confusion as shown by the arrangement of the terms in the following columns. Gaskell has used the term involuntary nervous system. Gray, sympathetic nervous system. Langley, autonomic nervous system. Meyer and Gottlieb, vegetative nervous system. Gray, craniosacral sympathetics. Langley, parasympathetics. Meyer and Gottlieb, autonomic. Gray, oculomotor sympathetics. Langley, tectal autonomics. Meyer and Gottlieb, cranial autonomics. Gray, facial sympathetics, glossopharyngeal sympathetics, vagal sympathetics. Langley, bulbar autonomics. Gray, sacral sympathetics. Langley, sacral autonomics. Meyer and Gottlieb, sacral autonomics. Gray, thoracolumbar sympathetics. Langley, sympathetic. Meyer and Gottlieb, sympathetic. Gray, enteric. Langley, thoracic autonomic. And enteric. Meyer and Gottlieb, enteric. The cranial sympathetics. The cranial sympathetics include sympathetic efferent fibers in the oculomotor, facial, glossopharyngeal and vagus nerves, as well as sympathetic afferent in the last three nerves. The sympathetic efferent fibers of the oculomotor nerve probably arise from cells in the anterior part of the oculomotor nucleus, which is located in the tegmentum of the midbrain. These preganglionic fibers run with the third nerve into the orbit and pass to the ciliary ganglion, where they terminate by forming synapses with sympathetic motor neurons whose axons, postganglionic fibers, proceed as the short ciliary nerves to the eyeball. Here they supply motor fibers to the ciliary muscle and the sphincter pupilae muscle. So far as known, there are no sympathetic afferent fibers connected with the nerve. The sympathetic efferent fibers of the facial nerve are supposed to arise from the small cells of the facial nucleus. According to some authors, the fibers to the ciliary glands arise from a special nucleus, the superior salivatory nucleus, consisting of cells scattered in a reticular formation dorsomedial to the facial nucleus. These preganglionic fibers are distributed partly through the cord of timpani and lingual nerve to the submaxillary ganglion, where they terminate about the cell bodies of neurons whose axons as postganglionic fibers conduct secretory and vasodilatory impulses to the submaxillary and sublingual glands. Other preganglionic fibers of the facial nerve pass via the great superficial patrosal nerve to the sphenopalantine ganglion, where they form synapses with neurons whose postganglionic fibers are distributed through the superior maxillary nerve, vasodilator and secretory fibers to the mucous membranes of the nose, soft palate, tongues, uveal, roof of the mouth, upper lips and gums, parodid and orbital glands. There are supposed to be a few sympathetic afferent fibers connected with the facial nerve, whose cell bodies lie in the geniculate ganglion, but very little is known about them. The sympathetic afferent fibers of the glossopharyngeal nerve pass either in the dorsal nucleus, nucleus ala saniria, or in a distinct nucleus, the inferior salivatory nucleus situated near the dorsal nucleus. These preganglionic fibers pass into the tympanic branch of the glossopharyngeal and then with the small superficial patrosal nerve to the odic ganglion. Postganglionic fibers, vasodilator and secretory fibers are distributed to the parodid gland to the mucous membrane and its glands on the tongue, the floor of the mouth and the lower gums. Sympathetic afferent fibers, whose cells of origin lie in the superior or inferior ganglion of the trunk, are supposed to terminate in the dorsal nucleus. Very little is known of the peripheral distribution of these fibers. The sympathetic efferent fibers of the vagus nerve are supposed to arise in the dorsal nucleus, nucleus ala saniria. These preganglionic fibers are all supposed to end in sympathetic ganglia situated in or near the organ supplied by the vagus sympathetics. The inhibitory fibers to the heart probably terminate in a small ganglia of the heart wall, especially the atrium, from which inhibitory postganglionic fibers are distributed to the musculature. The preganglionic motor fibers to the esophagus, the stomach, the small intestine and the greater part of the large intestine are supposed to terminate in the plexuses of ourbock, from which postganglionic fibers are distributed to the smooth muscles of these organs. Other fibers pass to the smooth muscles of the bronchial tree and to the gallbladder and its ducts. In addition, the vagus is believed to contain secretory fibers to the stomach and pancreas. It probably contains many other efferent fibers than those enumerated above. Sympathetic afferent fibers of the vagus, whose cells of origin lie in the jugular ganglion or the ganglion nodosum, probably terminate in the dorsal nucleus in the medulla oblongata or, according to some authors, in the nucleus of the tractus solitarius. Preferably, the fibers are supposed to be distributed to the various organs supplied by the sympathetic efferent nerves. The sacral sympathetics The sacral sympathetic efferent fibers leave the spinal cord with the anterior roots of the second, third and fourth sacral nerves. These small medulated preganglionic fibers are collected together in the pelvis into the nervous aerogentes, or pelvic nerve, which proceeds to the hypogastric or pelvic plexuses, from which postganglionic fibers are distributed to the pelvic viscera. Motor fibers pass to the smooth muscle of the descending colon rectum anus and bladder. Phasodilators are distributed to these organs and to the external genitalia, while inhibitory fibers probably pass to the smooth muscles of the external genitalia. Afferent sympathetic fibers conduct impulses from the pelvic viscera to the second, third and fourth sacral nerves. Their cells of origin lie in the spinal ganglia. The thoracolumbar sympathetics The thoracolumbar sympathetic fibers arise from the dorsolateral region of the anterior column of the gray matter of the spinal cord and pass with the anterior roots of all the thoracic and upper two or three lumbar spinal nerves. Enter the white ramea communicantes and proceed to the sympathetic trunk where many of them end in its ganglia. Others pass to the pre-vertebral plexuses and terminate in its collateral ganglia. The postganglionic fibers have a wide distribution. The vasoconstrictor fibers to the blood vessels of the skin of the trunk and limbs, for example, leave the spinal cord as preganglionic fibers in all the thoracic and upper two or three lumbar spinal nerves terminate in the ganglia of the sympathetic trunk either in the ganglion directly connected with its ramus or in neighboring ganglia. Postganglionic fibers arise in these ganglia, pass through the gray ramea communicantes to all the spinal nerves and are distributed with their cutaneous branches, ultimately leaving these branches to join the small arteries. The postganglionic fibers do not necessarily return to the same spinal nerves which contain the corresponding preganglionic fibers. The vasoconstrictor fibers to the head come from the upper thoracic nerves. The preganglionic fibers end in the superior cervical ganglion. The postganglionic fibers pass through the internal carotid nerve and branch from it to join the sensory branches of the various cranial nerves, especially the trigeminal nerve. Other fibers to the deep structures and the salivary glands probably accompany the arteries. The postganglionic vasoconstrictor fibers to the blood vessels of the abdominal viscera arise in the prevertebral or collateral ganglion in which terminate many preganglionic fibers. Vasoconstrictor fibers to the pelvic viscera arise from the inferior mesenteric ganglia. The pilomotor fibers to the hairs and the motor fibers to the sweat glands apparently have a distribution similar to that of the vasoconstrictors of the skin. A vasoconstrictor center has been located with a physiologist in the neighborhood of the facial nucleus. Axons from its cells are supposed to descend in the spinal cord to terminate about cell bodies of the preganglionic fibers located in the dorsolateral portion of the anterior column of the thoracic and upper lumbar region. The motor supply to the dilator pupillary muscle of the eye comes from preganglionic sympathetic fibers which leave the spinal cord with the anterior roots of the upper thoracic nerves. These fibers pass to the sympathetic trunks of the brain, ramea communicantes and terminate in the superior cervical ganglion. Postganglionic fibers from the superior cervical ganglion pass through the internal carotid nerve and into the ophthalmic division of the trigeminal nerve to the orbit where the long ciliary nerves conduct the impulses to the eyeball and dilator pupillary muscle. The cell bodies of these preganglionic fibers are connected with fibers which descend from the midbrain. secretory fibers to the salivary glands, the lacrimal glands, and to the small glands of the mucous membranes of the nose, mouth, and pharynx. The thoracic sympathetics apply accelerated nerves to the heart. They are supposed to emerge from the spinal cord in the anterior roots of the upper four or five thoracic nerves and pass with the white ramai to the first thoracic ganglion. Here some terminate, others pass in the ansus subclevia to the inferior cervical ganglion. The postganglionic fibers pass from these ganglia partly through the ansus subclevia to the heart. On their way they intermingle with sympathetic fibers from the vagus to form the cardiac plexus. Inhibitory fibers to the smooth musculature of the stomach, the small intestine, and most of the large intestine, are supposed to emerge in the anterior roots of the lower thoracic and upper lumbar nerves. These fibers pass through the white ramai and sympathetic trunk and are conveyed by the splanchnic nerves to the prevertebral plexus where they terminate in the collateral ganglion. From the celiac and superior mesenteric ganglia, postganglionic fibers, inhibitory, are distributed to the stomach, the small intestine, and most of the large intestine. Inhibitory fibers to the descending colon, the rectum, and the internal sphincter ani are probably postganglionic fibers from the inferior mesenteric ganglion. The thoracolumbar sympathetics are characterized by the presence of numerous ganglia which may be divided into two groups, central and collateral. The central ganglia are arranged in two vertical rows, one on either side of the midline, situated partly in front and partly at the sides of the vertebral column. Each ganglion is joined by intervening nervous cores to adjacent ganglia so that to change the sympathetic trunks are formed. The collateral ganglia are found in connection with the three great prevertebral plexuses placed within the thorax, abdomen, and pelvis respectively. The sympathetic trunks, truncus sympatheticus, gangliated cord, extend from the base of the skull to the coccyx. The cephalic end of each is continued upward through the carotid canal into the skull and forms a plexus on the internal carotid artery. The caudal ends of the trunk converge and end in a single ganglion, the ganglion impar placed in front of the coccyx. The ganglia of each trunk are distinguished as cervical, thoracic, lumbar, and sacral and, except in the neck, they are closely correspond the number to the vertebrae. They are arranged thus cervical portion three ganglia, thoracic portion twelve ganglia, lumbar portion four ganglia, sacral portion four or five ganglia. In the neck the ganglia lie in front of the transverse processes of the vertebrae, in the thoracic region in front of the heads of the ribs, in the lumbar region on the sides of the vertebral bodies, and in the sacral region in front of the sacrum. Connection with the spinal nerves. Communications are established between the sympathetic and spinal nerves through what are known as gray and white ramai communicantes. The gray ramai conveys sympathetic fibers to the spinal nerves and the white ramai transmits spinal fibers to the sympathetic. Each spinal nerve receives a gray ramus communicantes from the sympathetic trunk, but white ramai are not supplied by all the spinal nerves. White ramai derived from the first thoracic to the first lumbar nerves inclusive, while the visceral branches which run from the second, third, and fourth sacral nerves directly to the pelvic plexus of the sympathetic belong to this category. The fibers which reach the sympathetic through the white ramai cumina contes are medulated. Those which spring from the cells of the sympathetic ganglia are almost entirely non-medulated. The sympathetic nerves consist of efferent and afferent fibers, the origin and course of which are described subsequently. The three great gangliated plexuses, collateral ganglia, are situated in front of the vertebral column in the thoracic abdominal and pelvic regions, and are named respectively the cardiac, the solar or epigastric, and the hypogastric plexuses. They consist of a collection of nerves and ganglia, the nerve being derived from the sympathetic trunks and from the cerebrospinal nerves. They distribute branches to the viscera. Development. The ganglion cells of the sympathetic system are derived from the cells of the neural crests. As these crests move forward along the sides of the neural tube and become segmented off to form the spinal ganglia, certain cells detach themselves from the ventral margins of the crests and migrate towards the sides of the aorta. Some of them are grouped to form the ganglia of the sympathetic trunks, while others undergo a further migration and form the ganglia of the pre-vertebral and visceral plexuses. The ciliary, sphenopalantine, odic and submaxillary ganglia, which are found on the branches of the trigeminal nerve, are formed by groups of cells which have migrated from part of the neural crest, which gives rise to the semi-lunar ganglion. Some of the cells of the ciliary ganglion are said to migrate from the neural tube along the ocular motor nerve. End of section 43. Section 44 of Gray's Anatomy Part 4. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording from ML Cohen. Anatomy to Human Body Part 4 by Henry Gray. The cephalic and cervical portions of the sympathetic system. The cephalic portion of the sympathetic system. Parcecephalica. S. Sympathese. The cephalic portion of the sympathetic system begins as the internal carotid nerve, which appears to be a direct prolongation of the superior cervical ganglion. It is soft in texture and of a reddish color. It ascends by the side of the internal carotid artery, and entering the carotid canal in the temporal bone divides into two branches, which lie one on the lateral and the other on the medial side of that vessel. The lateral branch, the larger of the two, distributes filaments to the internal carotid artery and forms the internal carotid plexus. The medial branch also distributes filaments to the internal carotid artery and, continuing onward, forms the cavernous plexus. The internal carotid plexus, plexus caroticus internius carotid plexus, is situated on the lateral side of the internal carotid artery and in the plexus there occasionally exists a small ganglia-formed swelling, the carotid ganglion, on the under surface of the artery. The internal carotid plexus communicates with the semi-lunar ganglion, the abducent nerve, and the sphenopontine ganglion. It distributes filaments to the wall of the carotid artery and also communicates with the tympanic branch of the glossopharyngeal nerve. The communicating branches with the abducent nerve consist of one or two filaments which join that nerve as it lies upon the lateral side of the internal carotid artery. The communication with the sphenopalantine ganglion is affected by a branch, the deep protrosal, given off from the plexus on the lateral side of the artery. This branch passes through the cartilage filling up the frame in lecerum and joins the gradle superficial protrosal to form the nerve of the pteragoid canal, vidian nerve, which passes through the pteragoid canal to the sphenopontine ganglion. Communication with the tympanic branch of the glossopharyngeal nerve is affected by the corticotempanic, which may consist of two or three delicate filaments. The cavernous plexus, plexus cavernosis, is situated below and medial to that part of the internal carotid artery, which is placed by the side of the seletursica in the cavernous sinus and is formed chiefly by the medial division of the internal carotid nerve. It communicates with the ocular motor, the trochlear, the optomic, and the abducent nerves and with the ciliary ganglion and distributes filaments to the wall of the internal carotid artery. The branch of communication with the ocular motor nerve joins that nerve at its pointed division. The branch to the trochlear nerve joins it as it lies on the lateral wall of the cavernous sinus. Other filaments are connected with the undersurface of the optomic nerve and the second filament joins the abducent nerve. The filaments of connection with the ciliary ganglion arise from the anterior part of the cavernous plexus and enter the orbit through the superior orbital fissure. They may join the nasociliary branch of the optomic nerve or be continued forward as a separate branch. The terminal filaments from the internal carotid and cavernous plexuses are prolonged as plexuses around the anterior and middle cerebral arteries and the optomic artery. Along the formal vessels, they may be traced to the pia mater along the ladder into the orbit where they accompany each of the branches of the vessel. The filaments prolonged on to the anterior communicating artery connect the sympathetic nerves of the right and left sides. The cervical portion of the sympathetic system. Paraservicalis, S-sympathiesi. The cervical portion of the sympathetic trunk consists of three ganglia distinguished according to positions as the superior middle and inferior ganglia connected by intervening cords. This portion receives no white ramai communicantes from the cervical spinal nerves. Its spinal fibers are derived from the white ramai of the upper thoracic nerves and enter the corresponding thoracic ganglia of the sympathetic trunk through which they ascend into the neck. The superior cervical ganglion, ganglion cervicalis superioreus, the largest of the three, is placed opposite the second and third cervical vertebrae. It is of reddish gray color and usually fuses a form in shape sometimes broad and flattened and occasionally constricted at intervals. It is believed to be formed by the coalescence of four ganglia corresponding to the upper four cervical nerves. It is in relation in front with the sheath of the internal carotid artery and internal jugular vein. Behind with the longest capitis muscle. Its branches may be divided into inferior lateral, medial and anterior. The inferior branch communicates with the middle cervical ganglion. The lateral branches, external branches, consist of gray ramai communicantes to the upper four cervical nerves and a certain of the cranial nerves. Sometimes the branch to the fourth cervical nerve may come from the trunk connecting the upper and middle cervical ganglia. The branches to the cranial nerves consist of delicate filaments which run to the ganglion nodosum of the vagus and to the hypoglossal nerve. A filament, the jugular nerve, passes upward to the base of the skull and divides to join the petrus ganglion of the glossopharyngeal and the jugular ganglion of the vagus. The medial branches, internal branches, are peripheral and are the laryngopharyngeal branches and the superior cardiac nerve. The laryngopharyngeal branches, ramai laryngopharyngi, pass to the sides of the pharynx where they join with branches from the glossopharyngeal vagus and external laryngeal nerves to form the pharyngeal plexus. The superior cardiac nerve, nervous cardiacus superior, arises by two or more branches from the superior cervical ganglion and occasionally receives a filament from the trunk between the first and second cervical ganglia. It runs down the neck behind the common carotid artery and in front of the longest coli muscle and crosses in front of the inferior thyroid artery and recurrent nerve. The course of the nerves on the two sides then differ. The right nerve at the root of the neck passes either in front of or behind the subclavian artery and along the inominent artery to the back of the arch of the aorta where it joins the deep part of the cardiac plexus. It is connected with other branches of the sympathetic. About the middle of the neck it receives filaments from the external laryngeal nerve, lower down one or two twigs from the vagus and as it enters the thoracic it is joined by a filament from the recurrent nerve. Filaments from the nerve communicate with the thyroid branches from the middle cervical ganglion. The left nerve in the thorax runs in front of the left common carotid artery and across the left side of the arch of the aorta to the superficial part of the cardiac plexus. The anterior branches, nervous caroticy externi, remify upon the common carotid artery and upon the external carotid artery and its branches, forming around each a delicate plexus on the nerves composing which small ganglia are occasionally found. The plexuses accompanying some of these arteries have important communications with other nerves. That surrounding the external maxillary artery communicates with the submaxillary ganglia and by a filament and that accompanying the middle meningeal artery sends an offset to the odic ganglia and a second the external patrosal nerve to the genicular ganglion to the facial nerve. The middle cervical ganglion, ganglion cervicali media is the smallest of the three cervical ganglia and is occasionally wanting. It is placed opposite the six cervical vertebrae, usually in front of or close to the inferior thyroid artery. It is probably formed by the coalescence of two ganglia corresponding to the fifth and sixth cervical nerves. It sends gray ramaic communicantes to the fifth and sixth cervical nerves and gives off the middle's cardiac nerve. The middle cardiac nerve, nerve cardiacus medius, great cardiac nerve, is the largest of the three cardiac nerves, arises from the middle cervical ganglion or from the trunk between the middle and inferior ganglia. On the right side, it descends behind the common carotid artery and at the root of the neck runs either in front of or behind the subclavian artery. It then descends on the trachea, receives a few filaments from the recurrent nerve and joins the right half of the deep part of the cardiac plexus. In the neck, it communicates with the superior cardiac and recurrent nerves. On the left side, the middle cardiac nerve enters the chest between the left carotid and subclavian arteries and joins the left half of the deep part of the cardiac plexus. The inferior cervical ganglion, ganglion cervicali inferior, is situated between the base of the transverse process of the last cervical vertebra and the neck of the first rib on the medial side of the costoservical artery. Its form is irregular, it is larger in size than the proceeding and is frequently fused with the first thoracic ganglion. It is probably formed by the coalescence of two ganglia, which correspond to the seventh and eighth cervical nerves. It is connected to the middle cervical ganglion by two or more cords, one of which forms a loop around the subclavian artery and supplies offsets to it. This loop is named ansa subclavia, via senae. The ganglion sends gray ramite communicantes to the seventh and eighth cervical nerves. It gives off the inferior cardiac nerve and offsets to blood vessels. The inferior cardiac nerve, nervous cardiacus inferior, arise from either the inferior cervical or the first thoracic ganglion. It descends behind the subclavian artery and along the front of the trachea to join the deep part of the cardiac plexus. It communicates freely behind the subclavian artery with the recurrent nerve and the middle cardiac nerve. The offsets to blood vessels form plexuses on the subclavian artery and its branches. The plexus on the vertebra artery is continued on to the basilar, posterior cerebral, and cerebellar arteries. The plexus on the inferior thyroid artery accompanies the artery to the thyroid gland and communicates with the recurrent and external laryngeal nerves with the superior cardiac nerve and with the plexus on the common carotid artery. End of section 44. Section 45 of Gray's Anatomy, part 4. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit the LibriVox.org. Recording by David Lawrence. Anatomy of the Human Body, part 4, by Henry Gray. 7c. The Thoracic Portion of the Sympathetic System. Parz Thoracalis S. Sympathesy. The Thoracic Portion of the Sympathetic Trunk consists of a series of ganglia which usually correspond in number to that of the vertebrae but on account of the occasional coalescence of two ganglia their number is uncertain. The thoracic ganglia rests against the heads of the ribs and are covered by the costal pleura. The last two however are more anterior than the rest and are placed on the sides of the bodies of the 11th and 12th thoracic vertebrae. The ganglia are small in size and of a grayish color. The first, larger than the others, is of an elongated form and frequently blended with the inferior cervical ganglion. They are connected together by the intervening portions of the trunk. Two ramy communicantes, a white and a gray, connect each ganglia with its corresponding spinal nerve. The branches from the upper five ganglia are very small. They supply filaments to the thoracic artery and its branches. Twigs from the second, third, and fourth ganglia enter the posterior pulmonary plexus. The branches from the lower seven ganglia are large and white in color. They distribute filaments to the aorta and unite to form the greater, the lesser, and the lowest spanknic nerves. The greater spanknic nerve and spanknicus major, great spanknic nerve, his white in color, firm in texture, and of a considerable size. It is formed by branches from the fifth to the ninth or tenth thoracic ganglia. But the fibers in the higher roots may be traced upward in the sympathetic trunk, as far as the first or second thoracic ganglion. It descends obliquely on the bodies of the vertebrae, perforates the crusts of the diaphragm, and ends in the ciliac ganglion. A ganglion, ganglion splanchnicum, exists on this nerve opposite the 11th or 12th thoracic vertebra. The lesser spanknic nerve and spanknicus minor is formed by filaments from the ninth and 10th, and sometimes the 11th thoracic ganglia, and from the cord between them. It pierces the diaphragm with the preceding nerve and joins the aortic arena ganglion. The lower spanknic nerve, spanknicus imus, least spanknic nerve, arises from the last thoracic ganglion, and piercing the diaphragm ends in the renal plexus. A striking analogy exists between the spanknic and the cardiac nerves. The cardiac nerves are three in number. They arise from all three cervical ganglia, and are distributed to a large and important organ in the thoracic cavity. The spanknic nerves, also three in number, are connected probably with all the thoracic ganglia, and are distributed to important organs in the abdominal cavity. 7D, the abdominal portion of the sympathetic system. Pars abdominalis S sympathisi, lumbar portion of ganglionated cord. The abdominal portion of the sympathetic trunk is situated in front of the vertebral column, along the medial margin of the psoas major. It consists usually of four lumbar ganglia, connected together by interganglionic cords. It is continuous above with the thoracic portion beneath the medial lumbocostal arch, and below with the pelvic portion behind the common iliac artery. The ganglia are of small size and placed much near the median line, then are the thoracic ganglia. Gray rami cumunicantes pass from all the ganglia to the lumbar spinal nerves. The first and second, and sometimes the third lumbar nerves, sent white rami cumunicantes to the corresponding ganglia. The rami cumunicantes are of considerable length, and accompany the lumbar arteries around the sides of the bodies of the vertebrae. Passing beneath the fibrous arches from which some of the fibers of the psoas major arise. Of the branches of distribution, some pass in front of the aorta and join the aortic plexus. Others descend in front of the common iliac arteries and assist in forming the hypogastric plexus. Seven E. The pelvic portion of the sympathetic system. Parzfalvina S. Sympathesy. The pelvic portion of each sympathetic trunk is situated in front of the sacrum, medial to the interior sacral foramina. It consists of four or five small sacral ganglia, connected together by interganglionic cords and continuous above with the abdominal portion. Below the two pelvic sympathetic trunks converge and end on the front of the coccyx. In a small ganglion, the ganglion impar. Gray ramai communicantes pass from the ganglia to the sacral and the coccygeal nerves. No white ramai communicantes are given to this part of the ganglionated cord, but the visceral branches which arise from the third and fourth and sometimes from the second sacral and run directly to the pelvic plexuses are regarded as the white ramai communicantes. The branches of distribution communicate on the front of the sacrum with the corresponding branches from the opposite side. Some from the first two ganglia pass to join the pelvic plexus and others form a plexus which accompanies the middle sacral artery and sends filaments to the glumus coxegeum, coccygeal body. End of section 45. Recording by David Lawrence, October 2009 in Brampton, Ontario. Section 46 of Gray's Anatomy Part 4. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Bologna Times. Anatomy of the Human Body Part 4 by Henry Gray. The Great Plexuses of the Sympathetic System. The great plexuses of the sympathetic are aggregations of nerves and ganglia situated in the thoracic, abdominal, and pelvic cavities and named the cardiac, celiac, and hypogastric plexuses. They consist not only of sympathetic fibers derived from the ganglia but of fibers from the medulla spinalis which are conveyed through the white rame communicantes. From the plexuses, branches are given to the thoracic, abdominal, and pelvic viscera. The cardiac plexus. Plexus cardiacus. The cardiac plexus is situated at the base of the heart and is divided into a superficial part which lies in the concavity of the aortic arch and a deep part between the aortic arch and the trachea. The two parts are, however, closely connected. The superficial part of the cardiac plexus lies beneath the arch of the aorta in front of the right pulmonary artery. It is formed by the superior cardiac branch of the left sympathetic and the lower superior cervical cardiac branch of the left vegas. A small ganglion, the cardiac ganglion of Riesburg, is occasionally found connected with these nerves at their point of junction. This ganglion, when present, is situated immediately beneath the arch of the aorta on the right side of the ligamentum arteriosum. The superficial part of the cardiac plexus gives branches a to the deep part of the plexus, b to the anterior coronary plexus, and c to the left anterior pulmonary plexus. The deep part of the cardiac plexus is situated in front of the bifurcation of the trachea above the point of division of the pulmonary artery and behind the aortic arch. It is formed by the cardiac nerves derived from the cervical ganglia of the sympathetic and the cardiac branches of the vegas and recurrent nerves. The only cardiac nerves which do not enter into the formation of the deep part of the cardiac plexus are the superior cardiac nerve of the left sympathetic and the lower of the two superior cervical cardiac branches from the left vegas, which pass to the superficial part of the plexus. The branches from the right half of the deep part of the cardiac plexus pass, some in front of and others behind the right pulmonary artery. The former, the more numerous, transmit a few filaments to the anterior pulmonary plexus and are then continued onward to form part of the anterior coronary plexus. Those behind the pulmonary artery distribute a few filaments to the right atrium and are then continued onward to form part of the posterior coronary plexus. The left half of the deep part of the plexus is connected with the superficial part of the cardiac plexus and gives filaments to the left atrium and to the anterior pulmonary plexus and is then continued to form the greater part of the posterior coronary plexus. The posterior coronary plexus, plexus coronarius posterior left coronary plexus, is larger than the anterior and accompanies the left coronary artery. It is chiefly formed by filaments prolonged from the left half of the deep part of the cardiac plexus and by a few from the right half it gives branches to the left atrium and ventricle. The anterior coronary plexus, plexus coronarius anterior right coronary plexus is formed partly from the superficial and partly from the deep parts of the cardiac plexus. It accompanies the right coronary artery and gives branches to the right atrium and ventricle. The celiac plexus, plexus coeliacus, solar plexus. The celiac plexus, the largest of the three sympathetic plexuses, is situated at the level of the upper part of the first lumbar vertebra and is composed of two large ganglia, the celiac ganglia and a dense network of nerve fibers uniting them together. It surrounds the celiac artery and the root of the superior mesenteric artery. It lies behind the stomach and the elemental bursa in front of the crura of the diaphragm and the commencement of the abdominal aorta and between the supra renal glands. The plexus and the ganglia receive the greater and lesser splaconic nerves of both sides and some filaments from the right vagus and give off numerous secondary plexuses along the neighboring arteries. The celiac ganglia, ganglia celiacca, semi-lunar ganglia, are two large irregularly shaped masses having the appearance of lymph glands and placed one on either side of the middle line in front of the crura of the diaphragm close to the supra renal glands, that on the right side being placed behind the inferior vena cava. The upper part of each ganglion is joined by the greater splancic nerve, while the lower part, which is segmented off and named the aorta corino ganglion, receives the lesser splancic nerve and gives off the greater part of the renal plexus. The secondary plexuses bringing from or connected with the celiac plexus are the frenic, renal, hepatic, spermatic, renal, superior mesenteric, superior gastric, abdominal aortic, supra renal, inferior mesenteric. The frenic plexus, plexus frenicus, accompanies the inferior frenic artery to the diaphragm. Some filaments passing to the supra renal gland. It arises from the upper part of the celiac ganglion and is larger on the right than on the left side. It receives one or two branches from the frenic nerve. At the point of junction of the right frenic plexus with the frenic nerve is a small ganglion, ganglion frenicum. This plexus distributes branches to the inferior vena cava and to the supra renal and hepatic plexuses. The hepatic plexus, plexus hepaticus, the largest offset from the celiac plexus, receives filaments from the left vagus and right frenic nerves. It accompanies the hepatic artery, ramifying upon its branches and upon those of the portal vein in the substance of the liver. Branches from this plexus accompany all the divisions of the hepatic artery. A considerable plexus accompanies the gastrodiodenal artery and is continued as the inferior gastric plexus on the right gastroepipleic artery along the greater curvature of the stomach, where it unites with offshoots from the lino plexus. The lino plexus, plexus linalis spleenic plexus is formed by branches from the celiac plexus, the left celiac ganglion, and from the right vagus nerve. It accompanies the lino artery to the spleen, giving off in its course subsidiary plexuses along the various branches of the artery. The superior gastric plexus gastricus superior gastric or coronary plexus accompanies the left gastric artery along the lesser curvature of the stomach and joins with branches from the left vagus. The supra renal plexus, plexus supra renalis is formed by branches from the celiac plexus, from the celiac ganglion, and from the phrenic and greater splanckic nerves, a ganglion being formed at the point of junction with the latter nerve. The plexus supplies the supra renal gland, being distributed chiefly to its medullary portion. Its branches are remarkable for their large size in comparison with that of the organ they supply. The renal plexus, plexus renalis, is formed by filaments from the celiac plexus. The aortic plexus is joined also by the smallest planckic nerve. The nerves from these sources, 15 or 20 in number, have a few ganglia developed upon them. They accompany the branches of the renal artery into the kidney. Some filaments are distributed to the spermatic plexus and on the right side to the inferior vena cava. The spermatic plexus, plexus spermaticus, is derived from the renal plexus, receiving branches from the aortic plexus. It accompanies the internal spermatic artery to the testes. In the female, the ovarian plexus, plexus arteria ovaricae, arises from the renal plexus and is distributed to the ovary and fundus of the uterus. The superior mesenteric plexus, plexus mesentericus superior, is a continuation of the lower part of the celiac plexus, receiving a branch from the junction of the right vagus nerve with the plexus. It surrounds the superior mesenteric artery, accompanies it into the mesenteri, and divides into a number of secondary plexuses, which are distributed to all parts supplied by the artery vis, pancreatic branches to the pancreas, intestinal branches to the small intestine, and ileocolic, right colic, and middle colic branches, which supply the corresponding parts of the great intestine. The nerves composing this plexus are white in color and firm in texture. In the upper part of the plexus, close to the origin of the superior mesenteric artery, is a ganglion, ganglion mesentericum superius. The abdominal aortic plexus, plexus aorticus abdominalis aortic plexus, is formed by branches derived on either side from the celiac plexus and ganglia, and receives filaments from some of the lumbar ganglia. It is situated upon the sides and front of the aorta, between the origins of the superior and inferior mesenteric arteries. From this plexus arise part of this bermatic, the inferior mesenteric and the hypogastric plexuses. It also distributes filaments to the inferior vena cava. The inferior mesenteric plexus, plexus mesentericus inferior, is derived chiefly from the aortic plexus. It surrounds the inferior mesenteric artery and divides into a number of secondary plexuses which are distributed to all the parts supplied by the artery vis, the left colic and sigmoid plexuses, which supply the descending and sigmoid parts of the colon, and the superior hemorrhoidal plexus, which supplies the rectum and joins in the pelvis with branches from the pelvic plexuses. The hypogastric plexus, plexus hypogastricus. The hypogastric plexus is situated in front of the last lumbar vertebra and the promontory of the sacrum, between the two common iliac arteries, and is formed by the union of numerous filaments, which descend on either side from the aortic plexus and from the lumbar ganglia. It divides below into two lateral portions, which are named the pelvic plexuses. The pelvic plexuses. The pelvic plexuses supply the viscera of the pelvic cavity and are situated at the sides of the rectum in the male, and at the sides of the rectum and vagina in the female. They are formed on either side by a continuation of the hypogastric plexus, by the sacral sympathetic efferent fibers from the second, third, and fourth sacral nerves, and by a few filaments from the first two sacral ganglia. At the points of junction of these nerves, small ganglia are found. From these plexuses, numerous branches are distributed to the viscera of the pelvis. They accompany the branches of the hypogastric artery. The middle hemorrhoidal plexus, plexus hemorrhoidal medias, arises from the upper part of the pelvic plexus. It supplies the rectum and joins the branches of the superior hemorrhoidal plexus. The vesicle plexus, plexus vesicalis, arises from the forepart of the pelvic plexus. The nerves composing it are numerous and contain a large proportion of spinal nerve fibers. They accompany the vesicle arteries and are distributed to the sides and fundus of the bladder. Numerous filaments also pass to the vesicle, seminalis and ductus deferentes. Those accompanying the ductus deferens join on the spermatic cord with branches from the spermatic plexus. The prosthetic plexus, plexus prostaticus, is continued from the lower part of the pelvic plexus. The nerves composing it are of large size. They are distributed to the prostate vesicule and the carpora cavernosa of the penis and urethra. The nerves supplying the carpora cavernosa consist of two sets, the lesser and greater cavernous nerves, which arise from the forepart of the prosthetic plexus and, after joining with branches from the pudendal nerve, pass forward beneath the pubic arch. The lesser cavernous nerves, cavernosa penis menares, small cavernous nerves, perforate the fibers covering with the penis near its root. The greater cavernous nerve, cavernosa's penis major, large cavernous plexus, passes forward along the dorsum of the penis, joins with the dorsal nerve of the penis and is distributed to the carpora cavernosa. The vaginal plexus arises from the lower part of the pelvic plexus. It is distributed to the walls of the vagina to the erectile tissue of the vestibule and to the clitoris. The nerves composing this plexus contain, like the vesicle, a large proportion of spinal nerve fibers. The uterine plexus accompanies the uterine artery to the side of the uterus between the layers of the broad ligament. It communicates with the ovarian plexus. End of section 46 Section 47 of Gray's Anatomy, part 4 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by David Lawrence. Anatomy of the Human Body, part 4 by Henry Gray. The organs of the senses and the common entigament. The organs of the senses may be divided into A. Those of the special senses of taste, smell, sight, and hearing. And B. Those associated with the general sensations of heat, cold, pain, pressure, etc. One. The peripheral organs of the special senses. A. The organs of taste. Organon gustus. The peripheral gustatory, or taste organs, consist of certain modified epithelial cells arranged in flask-shaped groups termed gustatory caliculi, taste buds, which are found on the tongue and adjacent parts. The occupy nests in the stratified effilium and are present in large numbers on the sides of the papillae vality and to a less extent on their opposed walls. They are also found on the fungiform papillae over the back part and sides of the tongue and in the general epithelial covering of the same areas. They are very plentiful over the fimbri, lingui, and are also present on the under surface of the soft palate and on the posterior surface of the epiglottis. Structure. Each taste bud is flask-like in shape. It's broad base resting on the corium and its snack opening by an orifice. The gustatory pore between the cells of the epithelium. The bud is formed by two kinds of cells, supporting cells and gustatory cells. The supporting cells are mostly arranged like the staves of a cask and form an outer envelope for the bud. Some, however, are found in the interior of the bud between the gustatory cells. The gustatory cells occupy the central portion of the bud. They are spindle-shaped and each possesses a large spherical nucleus near the middle of the cell. The peripheral end of the cell terminates at the gustatory pore in a fine hair-like filament, the gustatory hair. The central process passes toward the deep extremity of the bud and their ends in single or broofricated varicostates. The nerve fibrils after losing their medullary sheaths enter the taste bud and end in fine extremities between the gustatory cells. Other nerve fibrils ramify between the supporting cells and terminate in fine extremities. These, however, are believed to be the nerves of ordinary sensation and not gustatory. Nerves of taste. The corda tempani nerve, derived from the sensory root of the facial, is the nerve of taste for the anterior two-thirds of the tongue. The nerve for the posterior third is the glostal pharyngeal. End of section 47, recording by David Lawrence in Brampton, Ontario, September 2009. Section 48 of Gray's Anatomy Part 4. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Anatomy of the human body Part 4 by Henry Gray. The organ of smell. Organon olfactorius, the nose. The peripheral olfactory organ or organ of smell consists of two parts. An outer, the external nose, which projects from the centre of the face and an internal, the nasal cavity, which is divided by a septum into right and left nasal chambers. The external nose, nasus externus, outer nose. The external nose is primital in form and its upper angle or root is connected directly with the forehead. Its free angle is termed the apex. Its base is perforated by two elliptical orifices, the nares, separated from each other by an anterior posterior septum, the columnna. The margins of the nares are provided with a number of stiff hairs or ribbercy, which arrest the passage of foreign substances carried with the current of air intended for respiration. The lateral surfaces of the nose form, by their union in the middle line, the dorsum nasi, the direction of which varies considerably in different individuals. The upper part of the dorsum is supported by the nasal bones and is named the bridge. The lateral surface ends below in a rounded eminence, the ala nasi. Structure. The framework of the external nose is composed of bones and cartilages. It is covered by the integument and lined by mucus membrane. The bony framework occupies the upper part of the organ. It consists of the nasal bones and the frontal processes of the maxili. The cartilaginous framework, cartilaginous nasi consists of five large pieces, namely the cartilage of the septum, the two lateral and the two greater alar cartilages, and several smaller pieces, the lesser alar cartilages. The various cartilages are connected to each other and to the bones by a tough fibrous membrane. The cartilage of the septum, cartilaginous septi nasi, is somewhat quadrilateral in form, thicker at its margins than at its center, and completes the separation between the nasal cavities in front. Its anterior margin, thickest above, is connected with the nasal bones and is continuous with the anterior margins of the lateral cartilages. Below it is connected to the medial crura of the greater alar cartilages by fibrous tissue. Its posterior margin is connected with the perpendicular plate of the ethmoid, its inferior margin, with the vomer and the palatine processes of the maxili. It may be prolonged backward, especially in children, as a narrow process, the sphenoidal process, for some distance between the vomer and the perpendicular plate of the ethmoid. The septal cartilage does not reach as far as the lowest part of the nasal septum. This is formed by the medial crura of the greater alar cartilages and by the skin. It is freely movable, and hence is termed the septum mobile nasi. The lateral cartilage, cartilaginous nasi lateralis, upper lateral cartilage, is situated below the inferior margin of the nasal bone and is flattened and triangular in shape. Its anterior margin is thicker than the posterior and is continuous above with the cartilage of the septum, but separated from it below by a narrow fissure. Its superior margin is attached to the nasal bone and the frontal process of the maxilla. Its inferior margin is connected by fibrous tissue with the greater alar cartilage. The greater alar cartilage, cartilagio alaris major, lower lateral cartilage, is a thin flexible plate situated immediately below the proceeding and bent upon itself in such a manner as to form the medial and lateral walls of the narus of its own side. The portion which forms the medial wall, cruse mediali, is loosely connected with the corresponding portion of the opposite cartilage, the two forming together with the thickened integument and sub adjacent tissue, the septum mobile nasi. The part which forms the lateral wall, cruse laterali, is curved to correspond with the ala of the nose. It is oval and flattened, narrow behind where it is connected with the frontal process of the maxilla by a tough fibrous membrane, in which are found three or four small cartilaginous plates, the lesser alar cartilages, cartilagines, alaris, minorities, sesamoid cartilages. Above it is connected by fibrous tissue to the lateral cartilage and front part of the cartilage of the septum. Below it falls short of the margin of the narus, the ala being completed by fatty and fibrous tissue covered by skin. In front the greater alar cartilages are separated by a notch which corresponds with the apex of the nose. The muscles acting on the external nose have been described in the section on myology. The entanglement of the dorsum and size of the nose is thin and loosely connected with the sub adjacent parts, but over the tip and alae it is thicker and more firmly adherent and is furnished with a larger number of sebaceous follicles, the orifices of which are usually very distinct. The arteries of the external nose are the alar and septal branches of the external maxillary which supply the alae and septum, the dorsum and size being supplied from the dorsal nasal branch of the ophthalmic and the infer orbital branch of the internal maxillary, the veins end in the anterior, facial and ophthalmic veins. The nerves for the muscles of the nose are derived from the facial while the skin receives branches from the infertrochlear and nasociliary branches of the ophthalmic and from the infer orbital of the maxillary, the nasal cavity, cafum nasi, nasal fossa. The nasal chambers are situated one on either side of the median plane. They open in front through the nears and communicate behind through the colony with the nasal part of the pharynx. The nears are somewhat pear shaped apertures, each measuring about 2.5 centimeters, antero posteriori and 1.25 centimeters transversely at its widest part. The colony are two oval openings, each measuring 2.5 centimeters in the vertical and 1.25 centimeters in the transverse direction in a well-developed adult skull. For the description of the bony boundaries of the nasal cavity, see pages 194 and 195. Inside the aperture of the nostril is a slight dilation, the vestibule, bounded laterally by the ala and lateral cruise of the greater alar cartilage and medially by the medial cruise of the same cartilage. It is lined by skin containing hairs and sebaceous glands and extends as a small recess toward the apex of the nose. Each nasal cavity, above and behind the vestibule, is divided into two parts, an olfactory region consisting of the superior nasal conca and the opposed part of the septum and a respiratory region which comprises the rest of the cavity. Lateral wall On the lateral wall are the superior, middle and inferior nasal conca and below and lateral to each conca is the corresponding nasal passage or meatus. Above the superior conca is a narrow recess, the sphenoethmoidal recess into which the sphenoidal sinus opens. The superior meatus is a short oblique passage extending about halfway along the upper border of the middle conca. The posterior ethmoidal cells open into the front part of this meatus. The middle meatus is below and lateral to the middle conca and is continued anteriorly into a shallow depression situated above the vestibule and named the atrium of the middle meatus. Unraising or removing the middle conca, the lateral wall of this meatus is fully displayed. On it is a rounded elevation, the bula ethmoidalis and below and in front of this a curved cleft, the hiatus semi-linaris. The bula ethmoidalis is caused by the bulging of the middle ethmoidal cells which open on or immediately above it and the size of the bula varies with that of its contained cells. The hiatus semi-linaris is bounded inferiorly by the sharp concave margin of the unsonate process of the ethmoid bone and leads into a curved channel, the infundibulum, bounded above by the bula ethmoidalis and below by the lateral surface of the unsonate process of the ethmoid. The anterior ethmoidal cells open into the front part of the infundibulum and this in slightly over 50% of subjects is directly continuous with the frontonasal duct or passage leading from the frontal ercinus. But when the anterior end of the unsonate process fuses with the front part of the bula, this continuity is interrupted and the frontonasal duct then opens directly into the anterior end of the middle hiatus. Below the bula ethmoidalis and partly hidden by the inferior end of the unsonate process is the osteum maxillair or opening from the maxillary sinus. In a frontal section, this opening is seen to be placed near the roof of the sinus and accessory opening from the sinus is frequently present below the posterior end of the middle nasal conca. The inferior hiatus is below and lateral to the inferior nasal conca, the nasal lacrimal duct opens into this miatus under cover of the anterior part of the inferior conca. Medial wall The medial wall or septum is frequently more or less deflected from the median plane, thus lessening the size of one nasal cavity and increasing that of the other. Ridges or spurs of bone growing into one or other cavity from the septum are also sometimes present. Immediately over the incisive canal at the lower edge of the cartilage of the septum, a depression, the nasal palantine recess is seen. In the septum close to this recess a minute orifice may be discerned. It leads backward into a blind pouch, the rudimentary vomeronasal organ of Jacobson which is supported by a strip of cartilage, the vomeronasal cartilage. This organ is well developed in many of the lower animals where it apparently plays a part in the sense of smell since it is supplied by twigs of the olfactory nerve and lined by epithelium similar to that in the olfactory region of the nose. The roof of the nasal cavity is narrow from side to side except at its posterior part and may be divided from behind forward into sphenoidal, ethmoidal, and frontonasal parts after the bones which form it. The floor is concave from side to side and almost horizontal anteriorly. Its anterior three-fourths are formed by the palatine process of the maxilla. It's posterior fourth by the horizontal process of the palatine bone. In its anterior medial part directly over the incisive foramen, a small depression, the nasal palatine recess is sometimes seen. It points downward and forward and occupies the position of a canal which connected the nasal with debucal cavity in early fetal life. The mucous membrane, membrane mucosa nasi. The nasal mucous membrane lines the nasal cavities and is intimately adherent to the periosteum or pericondrium. It is continuous with the skin through the nares and with the mucous membrane of the nasal part of the pharynx through the coenae. From the nasal cavity its continuity with the conjunctiva may be traced through the nasal lacrimal and lacrimal ducts and with the frontal, ethmoidal, sphenoidal and maxillary sinuses through the several openings in the meatuses. The mucous membrane is thickest and most vascular over the nasal conchi. It is also thick over the septum but it is very thin in the meatuses on the floor of the nasal cavities and in the various sinuses. Owing to the thickness of the greater part of this membrane the nasal cavities are much narrower and the middle and inferior nasal conchi appear larger and more prominent than in the skeleton. Also the various apertures communicating with the meatuses are considerably narrowed. Structure of the mucous membrane The epithelium covering the mucous membrane differs in its character according to the functions of the part of the nose in which it is found. In the respiratory region it is columnar and ciliated. Interspersed among the columnar cells are goblet or musin cells while between their bases are found similar pyramidal cells. Beneath the epithelium and its basement membrane is a fibrous layer infiltrated with lymph corpuscles so as to form in many parts a diffuse adenoid tissue. And under this a nearly continuous layer of small and larger glands some mucous and some cirrus the ducts of which open upon the surface. In the olfactory region the mucous membrane is yellowish in color and the epithelial cells are columnar and non-ciliated. They are of two kinds supporting cells and olfactory cells. The supporting cells contain oval nuclei which are situated in the deeper parts of the cells and constitute the zone of oval nuclei. The superficial part of each cell is columnar and contains granules of yellow pigment while its deep part is prolonged as a delicate process which ramifies and communicates with similar processes from neighboring cells so as to form a network in the mucous membrane. Lying between the deep processes of the supporting cells are a number of bipolar nerve cells the olfactory cells each consisting of a small amount of granular protoplasm with a large spherical nucleus and possessing two processes a superficial one which runs between the columnar epithelial cells and projects on the surface of the mucous membrane as a fine hair-like process the olfactory hair the other or deep process runs inward is frequently beaded and is continued as the axon of an olfactory nerve fiber. Beneath the epithelium and extending through the thickness of the mucous membrane is a layer of tubular often branched glands the glands of Bowman identical in structure with cirrus glands the epithelial cells of the nose fosses and respiratory passages play an important part in the maintenance of an equitable temperature by the moisture with which they keep the surface always slightly lubricated. Vessels and Nerves The arteries of the nasal cavities are the anterior and posterior ethmoidal branches of the ophthalmic which supply the ethmoidal cells frontal sinuses and roof of the nose The sphenopalentine branch of the inferior maxillary which supplies the mucous membrane covering the conchi the meiasis and septum the septal branch of the superior labial of the external maxillary the infer orbital and alveolar branches of the internal maxillary which supply the lining membrane of the maxillary sinus and the pharyngeal branch of the same artery distributed to the sphenoidal sinus The ramifications of these vessels form a close plexiform network beneath and in the substance of the mucous membrane The veins form a close cavernous plexus beneath the mucous membrane This plexus is especially well marked over the lower part of the septum and over the middle and inferior conchi Some of the veins open into the sphenopalentine vein Others join the anterior facial vein Some accompany the ethmoidal arteries and end in the ophthalmic veins and lastly if you communicate with the veins on the orbital surface of the frontal lobe of the brain through the ferramina in the cribiform plate of the ethmoid bone when the ferramin cecum is patent it transmits a vein to the superior sagittal sinus The lymphatics have already been described page 695 The nerves of ordinary sensation are the nasal ciliary branch of the ophthalmic filaments from the anterior aviolar branch of the maxillary the nerve of the pterygoid canal the nasal palatine the anterior palatine and nasal branches of the sphenopalentine ganglion The nasal ciliary branch of the ophthalmic distributes filaments to the four part of the septum and lateral wall of the nasal cavity Filaments from the anterior aviolar nerve supply the inferior miatus and inferior concha The nerve of the pterygoid canal supplies the upper and back part of the septum and superior concha and the upper nasal branches from the sphenopalentine ganglion have a similar distribution The nasal palatine nerve supplies the middle of the septum The anterior palatine nerve supplies the lower nasal branches to the middle and inferior concha The olfactory the special nerve of the sense of smell is distributed to the olfactory region Its fibers arise from the bipolar olfactory cells and are destitute of medullary sheaths They unite in fasciculi which form a plexus beneath the mucous membrane and then ascend in grooves or canals in the ethmoid bone They pass into the skulls through the foramina in the cribiform plate of the ethmoid and enter the under surface of the olfactory bulb in which they ramify and form synapses with the dendrites of the mitral cells The accessory sinuses of the nose Sinus paranasalis The accessory sinuses or air cells of the nose are the frontal, ethmoidal, sphenoidal, and maxillary They vary in size and form in different individuals and are lined by ciliated mucous membrane directly continuous with that of the nasal cavities The frontal sinuses Sinus frontalis situated behind the supercillary arches are rarely symmetrical and the septum between them frequently deviates to one or other side of the middle line Their average measurements are as follows Height 3 centimeters Breath 2.5 centimeters Depth from before backward 2.5 centimeters Each opens into the anterior part of the corresponding middle meiatus of the nose through the frontal nasal duct which traverses the anterior part of the labyrinth of the ethmoid Absent at birth they are generally fairly well developed between the seventh and eighth years but only reach their full size after puberty The ethmoidal air cells cellulite ethmoidalis consist of numerous thin-walled cavities situated in the ethmoidal labyrinth and completed by the frontal, maxilla, lacrimal, sphenoidal, and palatine They lie between the upper parts of the nasal cavities and the orbits and are separated from these cavities by thin bony lamini On either side they are arranged in three groups anterior, middle, and posterior The anterior and middle groups open into the middle meiatus of the nose the former by way of the infundibulum the latter, on or above, the bula ethmoidalis The posterior cells open into the superior meiatus under cover of the superior nasal conca Sometimes one or more opens into the sphenoidal sinus The ethmoidal cells begin to develop during fetal life The sphenoidal sinuses sinus sphenoidalis contained within the body of the sphenoid vary in size and shape owing to the lateral displacement of the intervening septum they are rarely symmetrical The following are their average measurements vertical height 2.2 centimeters transverse breadth 2 centimeters antero-posterior depth 2.2 centimeters When exceptionally large, they may extend into the roots of the teragoid processes or great wings and may invade the basilar part of the occipital bone Each sinus communicates with the sphenoidal recess by means of an aperture in the upper part of its anterior wall They are present as minute cavities at birth but their main development takes place after puberty The maxillary sinus sinus maxillaris antrum of haimur The largest of the accessory sinuses of the nose is a pyramidal cavity in the body of the maxilla Its base is formed by the lateral wall of the nasal cavity and its apex extends into the zygomatic process Its roof or orbital wall is frequently ridged by the infer orbital canal while its floor is formed by the aviolar process and is usually 1.5 to 10 millimeters below the level of the floor of the nose Projecting into the floor are several conical elevations corresponding with the roots of the first and second molar teeth and in some cases, the floor is perforated by one or more of these roots The size of the sinus varies in different skulls and even on the two sides of the same skull The adult capacity varies from 9.5 cubic centimeters to 20 cubic centimeters average about 14.75 cubic centimeters The following measurements are those of an average size sinus vertical height opposite the first molar tooth 3.75 centimeters transverse breadth 2.5 centimeters antero-posterior depth 3 centimeters In the antero-superior part of its base is an opening through which it communicates with the lower part of the hiatus semilunaris A second orifice is frequently seen in or immediately behind the hiatus The maxillary sinus appears as a shallow groove on the medial surface of the bone about the fourth month of fetal life but does not reach its full size until after the second dentition Footnote The various measurements of the accessory sinuses of the nose are based on those given by Aldrin Turner in his accessory sinuses of the nose and a footnote At birth it measures about 7 millimeters in the dorsal ventral direction and at 20 months about 20 millimeters End of section 48 Section 49 of Gray's Anatomy Part 4 This is a LubriVox recording All LubriVox recordings are in the public domain For more information or to volunteer please visit LubriVox.org Read by Laurie Ann Walden Anatomy of the Human Body Part 4 by Henry Gray The organ of sight Organin visis the eye The bulb of the eye bulbous oculi, eyeball, or organ of sight is contained in the cavity of the orbit where it is protected from injury and moved by the ocular muscles Associated with it are certain accessory structures These are the muscles, fascia, eyebrows, eyelids, conjunctiva, and lacrimal apparatus The bulb of the eye is embedded in the fat of the orbit but is separated from it by a thin membranous sac the fascia bulbi It is composed of segments of two spheres of different sizes The anterior segment is one of a small sphere It is transparent and forms about one-sixth of the bulb It is more prominent than the posterior segment which is one of a larger sphere and is opaque and forms about five-sixth of the bulb The term anterior pole is applied to the central point of the anterior curvature of the bulb and that of posterior pole to the central point of its posterior curvature A line joining the two poles forms the optic axis The axes of the two bulbs are nearly parallel and therefore do not correspond to the axes of the orbits which are directed forward and lateralward The optic nerves follow the direction of the axes of the orbits and are therefore not parallel Each enters its eyeball three millimeters to the nasal side and a little below the level of the posterior pole The bulb measures rather more in its transverse and anteroposterior diameters than in its vertical diameter The former amounting to about 24 millimeters The latter to about 23.5 millimeters In the female, all three diameters are rather less than in the male Its anteroposterior diameter at birth is about 17.5 millimeters and at puberty from 20 to 21 millimeters Development The eyes begin to develop as a pair of diverticula from the lateral aspects of the forebrain These diverticula make their appearance before the closure of the anterior end of the neural tube After the closure of the tube, they are known as the optic vesicles They project toward the sides of the head and the peripheral part of each expands to form a hollow bulb while the proximal part remains narrow and constitutes the optic stalk The ectoderm overlying the bulb becomes thickened, invaginated and finally severed from the ectodermal covering of the head as a vesicle of cells, the lens vesicle which constitutes the rudiment of the crystalline lens The outer wall of the bulb becomes thickened and invaginated and the bulb is thus converted into a cup, the optic cup consisting of two strata of cells These two strata are continuous with each other at the cup margin which ultimately overlaps the front of the lens and reaches as far forward as the future aperture of the pupil The invagination is not limited to the outer wall of the bulb but involves also its posterior inferior surface and extends in the form of a groove for some distance along the optic stalk so that, for a time, a gap or fissure, the caroidal fissure, exists in the lower part of the cup Through the groove and fissure, the mesoderm extends into the optic stalk and cup and in this mesoderm, a blood vessel is developed During the seventh week, the groove and fissure are closed and the vessel forms the central artery of the retina Sometimes the caroidal fissure persists and when this occurs, the caroid and iris in the region of the fissure remain undeveloped giving rise to the condition known as colaboma of the caroid or iris The retina is developed from the optic cup The outer stratum of the cup persists as a single layer of cells which assume a columnar shape, acquire pigment, and form the pigmented layer of the retina The pigment first appears in the cells near the edge of the cup The cells of the inner stratum proliferate and form a layer of considerable thickness from which the nervous elements and the sustentacular fibers of the retina, together with a portion of the vitreous body, are developed And that portion of the cup, which overlaps the lens, the inner stratum is not differentiated into nervous elements but forms a layer of columnar cells, which is applied to the pigmented layer And these two strata form the pars ciliares and pars eridica retini The cells of the inner or retinal layer of the optic cup become differentiated into spongioblasts and germinal cells And the latter, by their subdivisions, give rise to neuroblasts From the spongioblasts, the sustentacular fibers of Mueller, the outer and inner limiting membranes, together with the groundwork of the molecular layers of the retina are formed The neuroblasts become arranged to form the ganglionic and nuclear layers The layer of rods and cones is first developed in the central part of the optic cup And from there gradually extends toward the cup margin All the layers of the retina are completed by the eighth month of fetal life The optic stalk is converted into the optic nerve by the obliteration of its cavity and the growth of nerve fibers into it Most of these fibers are centripetal and grow backward into the optic stalk from the nerve cells of the retina, but a few extend in the opposite direction and are derived from nerve cells in the brain The fibers of the optic nerve receive their medullary sheaths about the 10th week after birth The optic chiasma is formed by the meeting and partial decussation of the fibers of the two optic nerves Behind the chiasma the fibers grow backward as the optic tracks to the thalamine and midbrain The crystalline lens is developed from the lens vesicle which recedes within the margin of the cup and becomes separated from the overlying ectoderm by mesoderm The cells forming the posterior wall of the vesicle lengthen and are converted into the lens fibers which grow forward and fill up the cavity of the vesicle The cells forming the anterior wall retain their cellular character and form the epithelium on the anterior surface of the adult lens By the second month the lens is invested by a vascular mesodermal capsule the capsula vasculosa lentus The blood vessels supplying the posterior part of this capsule are derived from the hyaloid artery those for the anterior part from the anterior ciliary arteries The portion of the capsule which covers the front of the lens is named the pupillary membrane By the sixth month all the vessels of the capsule are atrophied except the hyaloid artery which disappears during the ninth month The position of this artery is indicated in the adult by the hyaloid canal which reaches from the optic disc to the posterior surface of the lens With the loss of its blood vessels the capsula vasculosa lentus disappears but sometimes the pupillary membrane persists at birth giving rise to the condition termed congenital atresia of the pupil The vitreous body is developed between the lens and the optic cup The lens rudiment and the optic vesicles are at first in contact with each other but after the closure of the lens vesicle and the formation of the optic cup the former withdraws itself from the retinal layer of the cup The two however remain connected by a network of delicate protoplasmic processes This network derived partly from the cells of the lens and partly from those of the retinal layer of the cup constitutes the primitive vitreous body At first these protoplasmic processes spring from the whole of the retinal layer of the cup but later are limited to the ciliary region where by a process of condensation they appear to form the zona ciliaris The mesoderm which enters the cup through the coroidal fissure and around the equator of the lens becomes intimately united with this reticular tissue and contributes to form the vitreous body which is therefore derived partly from the ectoderm and partly from the mesoderm The anterior chamber of the eye appears as a cleft in the mesoderm separating the lens from the overlying ectoderm The layer of mesoderm in front of the cleft forms the substantial propria of the cornea that behind the cleft the stroma of the iris and the pupillary membrane The fibers of the ciliary muscle are derived from the mesoderm but those of the sphincter and dilatator pupuli are of ectodermal origin being developed from the cells of the pupillary part of the optic cup The sclera and coroid are derived from the mesoderm surrounding the optic cup The eyelids are formed as small cutaneous folds which about the middle of the third month come together and unite in front of the cornea They remain united until about the end of the sixth month The lacrimal sac and nasolacrimal duct result from a thickening of the ectoderm in the groove naso-optic furrow between the lateral nasal and maxillary processes This thickening forms a solid cord of cells which sinks into the mesoderm During the third month the central cells of the cord break down and illumine the nasolacrimal duct is established The lacrimal ducts arise as buds from the upper part of the cord of cells and secondarily establish openings puncta lacrimalia on the margins of the lids The epithelium of the cornea and conjunctiva and that which lines the ducts and alveoli of the lacrimal gland are of ectodermal origin as are also the eyelashes and the lining cells of the glands which open on the lid margins End of section 49 Section 50 of Grey's Anatomy Part 4 This is a LibriVox recording All LibriVox recordings are in the public domain For more information or to volunteer please visit LibriVox.org Recording by Morgan Scorpion Anatomy of the Human Body Part 4 by Henry Gray Tunics of the Eye Part 1 From without inward the three tunics are 1. A fibrous tunic consisting of the sclera behind and the cornea in front 2. A vascular pigmented tunic comprising from behind forward the coroid, ciliary body and iris and 3. A nervous tunic, the retina 4. The fibrous tunic, tunica fibrosa oculi The sclera and cornea form the fibrous tunic of the bulb of the eye The sclera is opaque and constitutes the posterior 5 sixths of the tunic The cornea is transparent and forms the anterior sixth The sclera The sclera has received its name from its extreme density and hardness It is a firm, unyielding membrane serving to maintain the form of the bulb It is much thicker behind than in front The thickness of its posterior part is 1mm Its external surface is of white colour and is in contact with the inner surface of the fascia of the bulb It is quite smooth, except at the points where the recti and obliquy are inserted into it Its anterior part is covered by the conjunctival membrane Its inner surface is brown in colour and marked by grooves in which the ciliary nerves and vessels are lodged It is separated from the outer surface of the coroid by an extensive lymph space Spatium pericorioideal, which is transversed by an exceedingly fine cellular tissue, the laminar supracoroid dea Behind it is pierced by the optic nerve, and is continuous through the fibrous sheath of this nerve with the duomata Where the optic nerve passes through the sclera, the latter forms a thin, crib reform laminar, the laminar cribrosus sclerae The minute orifices in this laminar serve for the transmission of the nervous filaments, and the fibrous septa dividing them from one another are continuous with the membranous processes which separate the bundles of nerve fibres One of these openings, larger than the rest, occupies the centre of the laminar It transmits the central artery and the vein of the retina Around the entrance of the optic nerve are numerous small apertures for the transmission of the ciliary vessels and nerves, and about midway between this entrance and the sclerocorneal junction are four or five large apertures for the transmission of veins In front, the sclera is directly continuous with the cornea, the line of union being termed the sclerocorneal junction In the inner part of the sclera close to this junction is a circular canal, the sinus venousus sclerae, canal of schlem In a meridional section of this region, this sinus presents the appearance of a cleft, the outer wall of which consists of the firm tissue of the sclera, while its inner wall is formed by a triangular mass of trabecular tissue The apex of the mass is directed forward and is continuous with the posterior elastic laminar of the cornea The sinus is lined by endothelium and communicates externally with the anterior ciliary veins The aqueous humour drains into the sclera sinuses by passage through the pectinate villi, which are analogous in structure and function to the arachnoid villi of the cerebral meninges Structure The sclera is formed of white fibres tissue intermixed with fine elastic fibres, flattened connective tissue corpuscles, some of which are pigmented, are contained in cell spaces between the fibres The fibres are aggregated into bundles, which are arranged chiefly in a longitudinal direction Its vessels are not numerous, the capillaries being of small size, uniting at long and wide intervals Its nerves are derived from the ciliary nerves, but their exact mode of ending is not known The cornea The cornea is the projecting, transparent part of the external tunic, and forms the anterior sixth of the surface of the bulb It is almost circular in outline, occasionally a little broader in the transverse than in the vertical direction It is convex anteriorly and projects like a dome in front of the sclera Its degree of curvature varies in different individuals, and in the same individual at different periods of life, being more pronounced in youth than in advanced life The cornea is dense and of uniform thickness throughout, its posterior surface is perfectly circular in outline, and exceeds the anterior surface slightly in diameter Immediately in front of the sclera corneal junction, the cornea bulges inward as a thickened rim, and behind this there is a distinct furrow between the attachment of the iris and the sclera corneal junction This furrow has been named by Arthur Thompson The sulcus circularis corneae, it is bounded externally by the trabecular tissue already described as forming the inner wall of the sinus venousus sclerae Between this tissue and the anterior surface of the attached margin of the iris is an angular recess named the iridial angle or filtration angle of the eye Immediately outside the filtration angle is a projecting rim of sclera tissue which appears in a meridional section as a small triangular error termed the sclera spur Its base is continuous with the inner surface of the sclera immediately to the outer side of the filtration angle and its apex is directed forward and inward To the anterior sloping margin of this spur are attached the bundles of trabecular tissue just referred to From its posterior margin the meridional fibres of the sclerae muscle arise Structure The cornea consists from the fore-backward of four layers vis, one the corneal epithelium, continuous with that of the conjunctiva two the substantia propria three the posterior elastic lamina and four the endothelium of the anterior chamber The corneal epithelium epithelium cornei anterior layer covers the front of the cornea and consists of several layers of cells The cells of the deepest layer are columnar then followed two or three layers of polyhedral cells the majority of which are prickle cells similar to those found in the stratum mucosum of the cuticle Lastly there are three or four layers of squamous cells with flattened nuclei The substantia propria is fibrous, tough, unyielding and perfectly transparent It is composed of about 60 flattened lamellae superimposed one on another These lamellae are made up of bundles of modified connective tissue the fibres of which are directly continuous with those of the sclera The fibres of each lamella are for the most part parallel with one another but at right angles to those of adjacent lamellae fibres however frequently pass from one lamellae to the next The lamellae are connected with each other by an interstitial cement substance in which are spaces the corneal spaces these are stellate in shape and communicate with one another by numerous offsets each contains a cell the corneal corpuscle resembling in form the space in which it is lodged but not entirely filling it The layer immediately beneath the corneal epithelium presents certain characteristics which have led some anatomists to regard it as a distinct membrane and it has been named the anterior elastic lamina lamina elastica anterior anterior limiting layer bolmans membrane it differs however from the posterior elastic lamina in presenting evidence of fibra structure and in not having the same tendency to curl inward or to undergo fracture when detached from the other layers of the cornea it consists of extremely closely interwoven fibrils similar to those found in the substantia propria but contains no corneal corpuscles it may be regarded as a condensed part of the substantia propria the posterior elastic lamina lamina elastica posterior membrane of descomit membrane of demorph covers the posterior surface of the substantia propria and is an elastic transparent homogeneous membrane of extreme thinness which is not rendered opaque for either water alcohol or acids when stripped from the substantia propria it curls up or rolls upon itself with the attached surface innermost at the margin of the cornea the posterior elastic lamina breaks up into fibres which form the trabecular tissue already described the spaces between the trabeculi are termed the spaces of the angles of the iris spaces of fontana they communicate with the sinus venous scleri and with the anterior chamber at the filtration angle some of the fibres of this trabecular tissue are continued into the subsets of the iris forming the pectinate ligament of the iris while others are connected with the forepart of the scleri and coroid the endothelium of the anterior chamber endothelium camerae anterioris posterior layer corneal endothelium covers the posterior surface of the elastic lamina is reflected onto the front of the iris and also lines the spaces of the angle of the iris it consists of a single stratum of polygonal flattened nucleated cells vessels and nerves the cornea is a non-vascular structure the capillary vessels ending in loops at its circumference are derived from the anterior scleri arteries lymphatic vessels have not yet been demonstrated in it but are represented by the channels in which the bundles of nerves run these channels are lined by an endothelium the nerves are numerous and are derived from the scleri nerves around the periphery of the cornea they form an annular plexus from which fibres enter the substantia propria they lose their medullary sheaths and ramifies throughout its substance in a delicate network and their terminal filaments form a firm and closer plexus on the surface of the cornea proper beneath the epithelium this is termed the subepithelial plexus and from it fibres are given off which ramify between the epithelial cells forming an intraepithelial plexus the vascular tunic tunica vascular oculi the vascular tunic of the eye is formed from behind forward by the coroid the scleri body and the iris the coroid invests the posterior five-sixth of the bulb and extends as far forward as the aura serata of the retina the scleri body connects the coroid to the circumference of the iris the iris is a circular diaphragm behind the cornea and presents near its center a rounded aperture the pupil the coroid coriodaea the coroid is a thin highly vascular membrane of a dark brown or chocolate color investing the posterior five-sixth of the globe it is pierced behind by the optic nerve and in this situation is firmly adherent to the sclerar it is thicker behind than in front its outer surface is loosely connected by the laminar supra coriodaea with the sclerar its inner surface is attached to the pigmented layer of the retina structure the coroid consists mainly of a dense capillary plexus and of small arteries and veins carrying blood to and returning it from this plexus on its external surface is a thin membrane the laminar supra coriodaea composed of delicate nonvascular lamellae each lamella consisting of a network of fine elastic fibers along which are branched pigment cells the spaces between the lamellae are lined by endothelium and open freely into the peric coroidal lymph space which in its turn communicates with the periscleral space by the perforations in the sclerar through which the vessels and nerves are transmitted internal to this laminar is the coroid proper consisting of two layers an outer composed of small arteries and veins with pigment cells interspersed between them and an inner consisting of a capillary plexus the outer layer laminar vasculosa consists in part of the larger branches of the short ciliary arteries which run forward between the veins before they bend inward to end in the capillaries blood is formed principally of veins named from their arrangement the veni vorticosi they converge to four or five equidistant trunks which pierce the sclerar about midway between the scleroconial junction and the entrance of the optic nerve interspersed between the vessels are dark star-shaped pigment cells the processes of which communicating with those of neighboring cells form a delicate network or stroma which toward the inner surface of the coroid loses its pigmentary character the inner layer laminar coriocapillaris consists of an exceedingly fine capillary plexus formed by the short ciliary vessels the network is closer and finer in the posterior than in the anterior part of the coroid about 1.25 centimeters behind the cornea its meshes become larger and are continuous with those of the ciliary processes these two laminae are connected by a stratum intermedium consisting of fine elastic fibers on the inner surface of the laminar coriocapillaris is a very thin structuralis or frankly fibrous membrane called the laminar basalis it is closely connected with the stroma of the coroid and separates it from the pigmentary layer of the retina one of the functions of the coroid is to provide nutrition for the retina and to convey vessels and nerves to the ciliary body and iris tapetum this name is applied to the outer and posterior part of the coroid which in many animals presents an iridescent appearance the ciliary body corpus ciliary the ciliary body comprises the orbicular ciliary the ciliary processes and the ciliary muscle the orbicular ciliary is a zone of about four millimeters in width directly continuous with the anterior part of the coroid it presents numerous ridges arranged in a radial manner the ciliary processes processes ciliary are formed by the inward folding of the various layers of the coroid i.e. the coroid proper and the lamina basalis and are received between corresponding folding of the suspensory ligament of the lens they are arranged in a circle and form a sort of thrill behind the iris around the margin of the lens they vary from 60 to 80 in number lie side by side and may be divided into large and small the former are about 2.5 millimeters in length and the latter consisting of about one third of the entire number are situated in spaces between them but without regular arrangement they are attached by their periphery to three or four of the ridges of the orbicular ciliary and are continuous with the layers of the coroid their opposite extremities are free and rounded and are directed toward the posterior chamber of the eyeball and circumference of the lens in front they are continuous with the periphery of the iris their posterior surfaces are connected with the suspensory ligament of the lens structure the ciliary processes are similar in structure to the coroid but the vessels are larger and have chiefly a longitudinal direction their posterior surfaces are covered by a bi-laminal layer of black pigment cells which is continued forward from the retina and is named the parse ciliaris retinae in the stroma of the ciliary processes there are also stellate pigment cells but these are not so numerous as in the coroid itself according to henderson the aqueous humor is a secretion formed by the active intervention of the epithelial cells lining the apices of the ciliary processes end of section 50