 Section 59 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 Morgan Scorpion. Anatomy of the Human Body, Part 4 by Henry Gray. The Internal Ear or Labyrinth, Part 1. 1-D4, The Internal Ear or Labyrinth. Oris Intona. The Internal Ear is the essential part of the organ of hearing, receiving the ultimate distribution of the auditory nerve. It is called the labyrinth from the complexity of its shape, and consists of two parts. The Osseous Labyrinth, a series of cavities within the petrous part of the temple bone, and the Membranous Labyrinth, a series of communicating membranous sacs and ducts contained within the bony cavities. The Osseous Labyrinth, Labyrinthus Osseous. The Osseous Labyrinth consists of three parts, the vestibule, semicircular canals, and cochlea. These are cavities hollowed out of the substance of the bone and lined by periosteum. They contain a clear fluid, the perilymph, in which the membranous labyrinth is situated. The vestibule, vestibulum. The vestibule is the central part of the Osseous Labyrinth, and is situated medial to the tympanic cavity behind the cochlea and in front of the semicircular canals. It is somewhat a rodent shape, but flattened transversely. It measures about five millimetres from before backward, and the same from above downward, and about three millimetres across. In its lateral or tympanic wall is the finestra vestibule, closed in the fresh state by the base of the stapes and annular ligament. On the medial wall at the forepart is a small circular depression, the recessus fericus, which is perforated at its anterior and inferior part by several minute holes, macular cribrosa media, for the passage of filaments of the acoustic nerve to the succule, and behind this depression is an oblique ridge, the crystal vestibule, the anterior end of which is named the pyramid of the vestibule. This ridge bifurcates below to enclose a small depression, the fossa cochlearis, which is perforated by a number of holes for the passage of filaments of the acoustic nerve which supply the vestibular end of the ductus cochlearis. At the hindre part of the medial wall is the orifice of the aqueductus vestibule, which extends to the posterior surface of the petrus portion of the temporal bone. It transmits a small vein, and contains a tubular prolongation of the membranous labyrinth, the ductus endolymphaticus, which ends in a cul-de-sac between the layers of the duramata within the cranial cavity. On the upper wall or roof is a transversely oval depression, the recessus ellipticus, separated from the recessus sphericus by the crystal vestibule already mentioned. The pyramid and adjoining part of the recessus ellipticus are perforated by a number of holes, macular cribrosa superior. The apertures in the pyramid transmit the nerves to the utricle, those in the recessus ellipticus the nerves to the ampullae of the superior and lateral semicircular ducts. Behind are the five orifices of the semicircular canals. In front is an elliptical opening, which communicates with the scala vestibuli of the cochlea. The bony semicircular canals. Canales semicircularis oceae. The bony semicircular canals are three in number, superior, posterior, and lateral, and are situated above and behind the vestibule. They are unequal in length, compressed from side to side, and each describes the greater part of the circle. Each measures about 0.8 mm in diameter, and presents a dilation at one end, called the ampullae, which measures more than twice the diameter of the tube. They open into the vestibule by five orifices, one of the apertures being common to two of the canals. The superior semicircular canal. Canales semicircularis superior. 15 to 20 mm in length is vertical indirection, and is placed transversely to the long axis of the petrus portion of the temporal bone, on the anterior surface of which its arch forms a round projection. It describes about two-thirds of a circle. Its lateral extremity is ampullated, and opens into the upper part of the vestibule. The opposite end joins with the upper part of the posterior canal to form the cruse commune, which opens into the upper and medial part of the vestibule. The posterior semicircular canal. Canales semicircularis posterior. Also vertical is directed backward, nearly parallel to the posterior surface of the petrus bone. It is the longest of the three, measuring from 18 to 22 mm. Its lower or ampullated end opens into the lower and back part of the vestibule, its upper into the cruse commune already mentioned. The lateral or horizontal canal, canales semicircularis lateralis, external semicircular canal, is the shortest of the three. It measures from 12 to 15 mm, and its arch is directed horizontally backward and lateralward. Thus each semicircular canal stands at right angles to the other two. Its ampullated end corresponds to the upper and lateral angle of the vestibule, just above the finestra vestibule, where it opens close to the ampullated end of the superior canal. Its opposite end opens at the upper and back part of the vestibule. The lateral canal of one ear is very nearly in the same plane as that of the other, while the superior canal of one ear is nearly parallel to the posterior canal of the other. The cochlea. The cochlea bears some resemblance to a common snail shell. It forms the anterior part of the labyrinth, is conical in form, and placed almost horizontally in front of the vestibule. Its apex, cupula, is directed forward and lateralward, with a slight inclination downward toward the upper and front part of the labyrinthic wall of the tympanic cavity. Its base corresponds with the bottom of the internal acoustic miatus, and is perforated by numerous apertures for the passage of the cochlea division of the acoustic nerve. It measures about 5 mm from base to apex, and its breadth across the base is about 9 mm. It consists of a conical shaped central axis, the modiolis, of a canal, the inner wall of which is formed by the central axis, wound spirally around it for two turns and three quarters. From the base to the apex, and of a delicate lamina, the osseous spiral lamina, which projects from the modiolis and, following the windings of the canal, partially subdivides it into two. In the recent state a membrane, the basilar membrane, stretches from the free border of this lamina to the outer wall of the bony cochlea and completely separates the canal into two passages, which, however, communicate with each other at the apex of the modiolis by a small opening named the helicotrema. The modiolis is the conical central axis, or pillar, of the cochlea. Its base is broad and appears at the bottom of the internal acoustic miatus, where it corresponds with the area cochlea. It is perforated by numerous orifices which transmit filaments of the cochlea division of the acoustic nerve. The nerves of the first tone and a half pass through the foramina of the tractus spiralis foraminosus, those for the apical tone, through the foramin centrale. The canals of the tractus spiralis foraminosus pass up through the modiolis and successively bend outward to reach the attached margin of the lamina spiralis ossea. Here they become enlarged and by their apposition form the spiral canal of the modiolis, which follows the course of the attached margin of the ossea spiral lamina and lodges the spiral ganglion, ganglion of corti. The foramin centrale is continued into a canal which runs up the middle of the modiolis to its apex. The modiolis diminishes rapidly in size in the second and succeeding coil. The bony canal of the cochlea takes two turns and three quarters around the modiolis. It is about 30 mm in length and diminishes gradually in diameter from the base to the summit, where it terminates in the cupula which forms the apex of the cochlea. The beginning of this canal is about 3 mm in diameter. It diverges from the modiolis toward the tympanic cavity and vestibule and presents three openings. One, the finestra cochleae communicates with the tympanic cavity. In the fresh steak this aperture is closed by the secondary tympanic membrane. Another, of an elliptical form, opens into the vestibule. The third is the aperture of the aqueductus cochleae leading to a minute funnel shaped canal which opens on the inferior surface of the petrus part of the temporal bone and transmits a small vein and also forms a communication between the subarachnoid cavity and the scarlet impani. The osseus spiral lamina, lamina spiralis ossea, is a bony shelf or ledge which projects from the modiolis into the interior of the canal and, like the canal, takes two and three-quarter turns around the modiolis. It reaches about half way toward the outer wall of the tube and partially divides its cavity into two passages or scalli of which the upper is named the scarlet vestibule, while the lower is termed the scarlet impani. Near the summit of the cochlea the lamina ends in a hook-shaped process, the hamulus laminae spiralis. This assists in forming the boundary of the small opening, the helicotrima, through which the two scarlete communicate with each other. From the spiral canal of the modiolis numerous canals pass outward through the osseus spiral lamina as far as its free edge. In the lower part of the first turn a second bony lamina, the secondary spiral lamina, projects inward from the outer wall of the bony tube. It does not, however, reach the primary osseus spiral lamina, so that if viewed from the vestibule, a narrow fissure, the vestibule fissure, is seen between them. The osseus labyrinth is lined by an exceedingly thin fibrosirus membrane. Its attached surface is rough and fibrous and closely adherent to the bone. Its free surface is smooth and pale, covered with a layer of epithelium and secretes a thin, limpid fluid, the perilymph. A delicate tubular process of this membrane is prolonged along the aqueduct of the cochlea to the inner surface of the duomata. The membranous labyrinth Labyrinthus membronicius The membranous labyrinth is lodged within the bony cavities just described and has the same general form as these. It is, however, considerably smaller and is partly separated from the bony walls by a quantity of fluid, the perilymph. In certain places it is fixed to the walls of the cavity. The membranous labyrinth contains fluid, the endolymph, and on its walls, the ramifications of the acoustic nerve are distributed. Within the osseus vestibule, the membranous labyrinth does not quite preserve the form of the bony cavity, but consists of two membranous sacs, the utricle and the saccule, the utricle utriculus. The utricle, the larger of the two, is of an oblong form, compressed transversely, and occupies the upper and back part of the vestibule, lying in contact with the recessus ellipticus and the part below it. That portion which is lodged in the recess forms a sort of pouch or cul-de-sac, the floor and anterior wall of which are thickened, and form the macular acoustica utriculi, which receives the utricular filaments of the acoustic nerve. The cavity of the utricle communicates behind with the semicircular ducts by five orifices. From its anterior wall is given off the ductus utricular sacularis, which opens into the ductus endolymphaticus. The saccule, sacculus. The saccule is the smaller of the two vestibular sacs. It is globular in form and lies in the recessus sphericus near the opening of the scarlet vestibule of the cochlea. Its anterior part exhibits an oval thickening, the macular acoustica saculi, to which are distributed the sacular filaments of the acoustic nerve. Its cavity does not directly communicate with that of the utricle. From the posterior wall a canal, the ductus endolymphaticus, is given off. This duct is joined by the ductus utricular sacularis, and then passes along the aqueductus vestibuli and ends in a blind pouch, sacus endolymphaticus, on the posterior surface of the petrus portion of the temple bone, where it is in contact with the duoromata. From the lower part of the saccule, a short tube, the canalis rhenions uphensin, passes downward and opens into the ductus cochlearis near its vestibular extremity. The semicircular ducts. Ductus semicircularis, membranus semicircular canals. The semicircular ducts are about one-fourth of the diameter of the osseous canals, but in number, shape and general form they are precisely similar, and each presents at one end an ampulla. They're opened by five orifices into the utricle, one opening being common to the medial end of the superior and the upper end of the posterior duct. In the ampulla, the wall is thickened and projects into the cavity as a fiddle-shaped, transversely placed elevation, the septum transversum, in which the nerves end. The utricle, saccule and semicircular ducts are held in position by numerous fibrous bands which stretch across the space between them and the bony walls. Structure. The walls of the utricle, saccule and semicircular ducts consist of three layers. The outer layer is a loose and flocculant structure, apparently composed of ordinary fibrous tissue containing blood vessels and some pigment cells. The middle layer, thicker and more transparent, forms a homogenous membrane, propria, and presents on its internal surface, especially in the semicircular ducts, numerous papilliform projections which, on the addition of acetic acid, exhibit an appearance of longitudinal fibrillation. The inner layer is formed of polygonal nucleated epithelial cells. In the maculi of the utricle and saccule and in the transverse septum of the ampulli of the semicircular ducts, the middle coat is thickened and the epithelium is columnar and consists of supporting cells and hair cells. The former are fusiform and their deep ends are attached to the membrane apropria, while their free extremities are united to form a thin cuticle. The hair cells are flask-shaped, and their deep, rounded ends do not reach the membrane apropria, but lie between the supporting cells. The deep part of each contains a large nucleus, while its more superficial part is granular and pigmented. The free end is surmounted by a long, tapering, hair-like filament which projects into the cavity. The filaments of the acoustic nerve enter these parts, and having pierced the outer and middle layers, they lose their medullary sheaths, and their axis cylinders ramify between the hair cells. Two rounded bodies, termed otoconia, each consisting of a mass of minute crystalline grains of carbonate of lime, held together in a mesh of gelatinous tissue, are suspended in the endolymph in contact with the free ends of her hairs projecting from the maculi. According to Bowman, the calcareous material is also sparingly scattered in the cells lining the ampullae of the semicircular ducts. End of Section 59 Section 60 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 The Internal Ear or Labyrinth Part 2 The Doctor's Cochlearis Membranous Cochlear, Scarlet Media The Doctor's Cochlearis consists of a spirally arranged tube enclosed in the bony canal of the cochlear and lying along its outer wall. As already stated, the osseous spiral lamina extends only part of the distance between the modiolus and the outer wall of the cochlear, while the basilar membrane stretches from its free edge to the outer wall of the cochlear and completes the roof of the scarlet impani. A second and more delicate membrane, the vestibular membrane, vicenari, extends from the thickened periosteum covering the osseous spiral lamina to the outer wall of the cochlear, where it is attached at some little distance above the outer edge of the basilar membrane. A canal is thus shut off between the scarlet impani below and the scarlet vestibuli above. This is the Doctor's Cochlearis or Scarlet Media. It is triangular on transverse section, its roof being formed by the vestibular membrane, its outer wall by the periosteum lining the bony canal, and its floor by the membrane of basilaris and the outer part of the lamina spiralis osseous. Its extremities are closed. The upper is termed the lagina and is attached to the cochlear at the upper part of the helicotrima. The lower is lodged in the recessus cochlearis of the vestibule. Near the lower end the Doctor's Cochlearis is brought into continuity with the succul by a narrow short canal, the canalis reunions of Henson. On the membrane of basilaris is situated the spiral organ of Quartii. The vestibular membrane is thin and homogenous and is covered on its upper and under surfaces by a layer of epithelium. The periosteum forming the outer wall of the Doctor's Cochlearis is greatly thickened and altered in character and is called the spiral ligament. It projects inward below as a triangular prominence, the basilar crest, which gives attachment to the outer edge of the basilar membrane. Immediately above the crest is a concavity, the sulcus spiralis extonus. The upper portion of the spiral ligament contains numerous capillary loops and small blood vessels and is termed the striovascularis. The osteospiral lamina consists of two plates of bone and between these are the canals for the transmission of the filaments of the acoustic nerve. On the upper plate of that part of the lamina, which is outside the vestibular membrane, the periosteum is thickened to form the limbus lamina spiralis. This ends externally in a concavity, the sulcus spiralis internus, which represents on section the form of the letter C. The upper part, formed by the overhanging extremity of the limbus, is named the vestibular lip. The lower part, prolonged and tapering, is called the tympanic lip and is perforated by numerous foramina for the passage of the cochlear nerves. The upper surface of the vestibular lip is intersected at right angles by a number of furrows, between which are numerous elevations. These present the appearance of teeth along the free surface and margin of the lip and have been named by huska, the auditory teeth. The limbus is covered by a layer of what appears to be squamous epithelium, but the deeper parts of the cells with their contained nuclei occupy the intervals between the elevations and between the auditory teeth. This layer of epithelium is continuous on the one hand with that lining the sulcus spiralis internus, and on the other with that covering the undersurface of the vestibular membrane. Basilar membrane. The basilar membrane stretches from the tympanic lip of the osteospiral lamina to the basilar crest and consists of two parts, an inner and an outer. The inner is thin and is named the zona arcuata. It supports the spiral organ of corti. The outer is thicker and striated and is termed the zona pectinata. The undersurface of the membrane is covered by a layer of vascular-connective tissue. One of the vessels in this tissue is somewhat larger than the rest and is named the vaspirale. It lies below corti's tunnel. The spiral organ of corti, organon spirale, corti, organ of corti, is composed of a series of epithelial structures placed upon the inner part of the basilar membrane. The more central of these structures are two rows of rod-like bodies, the inner and outer rods, or pillars of corti. The bases of the rods are supported on the basilar membrane, those of the inner row at some distance from those of the outer. The two rows inclined toward each other and, coming into contact above, enclose between them and the basilar membrane a triangular tunnel, the tunnel of corti. On the inner side of the inner rods is a single row of hair cells, and on the outer side of the outer rods, three or four rows of similar cells, together with certain supporting cells termed the cells of detus and hensin. The free ends of the outer hair cells occupy a series of apertures in a net-like membrane, the reticular membrane, and the entire organ is covered by the tectorial membrane. Rods of corti. Each of these consists of a base or foot plate and elongated part or body, and an upper end or head. The body of each rod is finely striated, but in the head there is an oval, non-striated portion which stains deeply with calming. Occupying the angles between the rods and the basilar membrane are nucleated cells which partly envelop the rods and extend onto the floor of corti's tunnel. These may be looked upon as the undifferentiated parts of the cells from which the rods have been formed. The inner rods number nearly six thousand, and their bases rest on the basilar membrane close to the tympanic lip of the sulcus spiralis internus. The shaft or body of each is sinuously curved and forms an angle of about sixty degrees with the basilar membrane. The head resembles the proximal end of the ulna, and presents a deep concavity which accommodates a convexity on the head of the outer rod. The head plate or portion overhanging the concavity overlaps the head plate of the outer rod. The outer rods, nearly four thousand in number, are longer and more obliquely set than the inner, forming with the basilar membrane an angle of about forty degrees. Their heads are convex internally. They fit into the concavitys on the heads of the inner rods and are continued outward as thin flattened plates, termed phalangeal processes, which unite with the phalangeal processes of dita cells to form the reticular membrane. Hair cells. The hair cells are short columnar cells. Their free ends are on a level with the heads of cortis rods, and each is surmounted by about twenty hairlight processes arranged in the form of a crescent with its concavity directed inward. The deep ends of the cells reach about half way along cortis rods, and each contains a large nucleus. In contact with the deep ends of the hair cells are the terminal filaments of the cochlear division of the acoustic nerve. The inner hair cells are arranged in a single row on the medial side of the inner rods, and their diameters being greater than those of the rods, it follows that each hair cell is supported by more than one rod. The free ends of the inner hair cells are encircled by a cuticular membrane which is fixed to the heads of the inner rods. Adjoining the inner hair cells are one or two rows of columnar supporting cells, which, in turn, are continuous with the cubicle cells lining the sulcus spirulus internus. The outer hair cells number about twelve thousand, and are nearly twice as long as the inner. In the basal coil of the cochlear they are arranged in three regular rows, in the apical coil, in four, somewhat irregular rows. Between the rows of the outer hair cells are rows of supporting cells, called the cells of detas. Their expanded bases are planted on the basal membrane, while the opposite end of each presents a clubbed extremity or phalangeal process. Immediately to the outer side of deta cells are five or six rows of columnar cells, the supporting cells of Henson. Their bases are narrow, while their upper parts are expanded and form a rounded elevation on the floor of the ductus cochlearis. The columnar cells, lying outside Henson cells, are termed the cells of Claudius. A space exists between the outer rods of Cauti and the adjacent hair cells. This is called the space of Newell. The rectangular lamina is a delicate framework perforated by rounded holes, which are occupied by the free ends of the outer hair cells. It extends from the heads of the outer rods of Cauti to the external row of the outer hair cells, and is formed by several rows of minute fiddle shaped cuticular structures, called phalanges, between which are circular apertures containing the free ends of the hair cells. The innermost row of phalanges consists of the phalangeal processes of the outer rods of Cauti. The outer rows are formed by the modified free ends of deta cells. Covering the sulcus spiralis in ternus, and the spiral organ of Cauti, is the tectorial membrane, which is attached to the limbus laminis spiralis close to the inner edge of the vestibular membrane. Its inner part is thin and overlies the auditory teeth of Hushka. Its outer part is stick, and along its lower surface, opposite the inner hair cells, is a clear band, named Henson's stripe, due to the intercrossing of its fibres. The lateral margin of the membrane is much thinner. Hardesty considers the tectorial membrane as the vibrating mechanism in the cochlea. It is inconceivably delicate and flexible, far more sensitively flexible in the transverse than in the longitudinal direction, and the readiness with which it bends when touched is beyond description. It is ectodermal in origin. It consists of fine, colourless fibres embedded in a transparent matrix. The matrix may be a variety of soft keratin, of a soft collaginous, semi-solid character with marked adhesiveness. The general transverse direction of the fibres inclines from the radius of the cochlea toward the apex. The acoustic nerve, nervous acousticus, auditory nerve, or nerve of hearing, divides near the bottom of the internal acoustic miatus into an anterior or cochlea and a posterior or vestibular branch. The vestibular nerve, nervous vestibularis, supplies the utricle, the saccule, and the ampullae of the semicircular ducts. On the trunk of the nerve, within the internal acoustic miatus, is a ganglion, the vestibular ganglion, ganglion of scarper. The fibres of the nerve arise from the cells of this ganglion. On the distal side of the ganglion, the nerve splits into a superior and inferior and posterior branch. The filaments of the superior branch are transmitted through the foramina in the area vestibularis superior and end in the macular of the utricle and in the ampullae of the superior and lateral semicircular ducts. Those of the inferior branch traverse the foramina in the area vestibularis inferior and end in the macular of the saccule. The posterior branch runs through the foramin singularae at the postor inferior part of the bottom of the miatus and divides into filaments for the supply of the ampullae of the posterior semicircular duct. The cochlear nerve, nervous cochlearis, divides into numerous filaments at the base of the modiolus. Those for the basal and middle coils pass through the foramina in the tractor spiralis foraminosis. Those for the apical coil through the canalis centralis, and the nerves bend outward to pass between the lamellae of the osseous spiral lamina. Occupying the spiral canal of the modiolus is the spiral gangon of the cochlear, gangon of corti, consisting of bipolar nerve cells which constitute the cells of origin of this nerve. Reaching the outer edge of the osseous spiral lamina, the fibres of the nerve pass through the foramina in the tympanic lip. Some end by arborising around the bases of the inner hair cells, while others pass between cortis wads and across the tunnel to end in a similar manner in relation to the outer hair cells. The cochlear nerve gives off a vestibular branch to supply the vestibular end of the ductus cochlearis. The filaments of this branch pass through the foramina in the fossa cochlearis. Vessels. The arteries of the labyrinth are the internal auditory from the basilar and the stylo mastoid from the posterior auricular. The internal auditory artery divides at the bottom of the internal acoustic meatus into two branches, cochlear and vestibular. The cochlear branch subdivides into 12 or 14 twigs which traverse the canals in the modiolus and are distributed in the form of a capillary network in the lamina spiralis and basilar membrane. The vestibular branches are distributed to the utricle, succul and semicircular ducts. The veins of the vestibule and semicircular canals accompany the arteries and, receiving those of the cochlear at the base of the modiolus, unite to form the internal auditory veins which end in the posterior part of the superior petrosal sinus or in the transverse sinus. End of section 60 Section 61 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 I. E. Peripheral Terminations of Nerves of General Sensations The peripheral terminations of the nerves associated with general sensations, i.e., the muscular sense and the senses of heat, cold, pain and pressure, are widely distributed throughout the body. These nerves may end free among the tissue elements or in special end organs where the terminal nerve filaments are enclosed in capsules. Free nerve endings occur chiefly in the epidermis and in the epithelium covering certain mucus membranes. They are well seen also in the stratified squamous epithelium of the corona and are also found in the root sheaths and papillae of the hairs and around the bodies of the pseudoriferous glands. When the nerve fiber approaches its termination, the medullary sheath suddenly disappears, leaving only the axis cylinder surrounded by the neurolema. After a time, the fiber loses its neurolema and consists only of an axis cylinder, which can be seen in preparation stained with chloride of gold to be made up of fine varicose fibrilli. Finally, the axis cylinder breaks up into its constituent fibrilli, which often present regular variscosities and anastomose with one another, and end in small knobs or discs between the epithelial cells. Under this heading may be classed the tactile discs described by Merkel as occurring in the epidermis of the pig snout, where the fibrilli of the axis cylinder end in cup-shaped discs in opposition with large epithelial cells. The special end organs exhibit great variety in size and shape, but have one feature in common, viz the terminal nerve fibrilli are enveloped by a capsule. Included in this group are the end bulbs of crouse, the corpuscles of grandry, of pachini, of golgi and mizoni, of Wagner and Meisner, and the neuro-tendinous and neuromuscular spindles. The end bulbs of crouse are minute cylindrical or oval bodies, consisting of a capsule formed by the expansion of the connective tissue sheath of emidulated fiber and containing a soft semi-fluid core in which the axis cylinder terminates either in a bulbous extremity or in a coiled-up plexiform mass. End bulbs are found in the conjunctiva of the eye, where there are spheroidal in shape in man, but cylindrical in most other animals. In the mucous membrane of the lips and tongue and in the epineurium of nerve trunks, they are also found in the penis and the clitoris and have received the name of genital corpuscles. In these situations they have a mulberry-like appearance being constricted by connective tissue septa into from two to six knob-like masses. In the synovial membranes of certain joints, e.g. those of the fingers, rounded or oval end bulbs occur and are designated articular end bulbs. The tactile corpuscles of grandi occur in the papillae of the beak and tongue of birds. Each consists of a capsule composed of a very delicate, nucleated membrane and contains two or more granular, somewhat flattened cells between these cells the axis cylinder ends in flattened discs. The pechinian corpuscles are found in the subcutaneous tissue on the nerves of the palm of the hand and sole of the foot and in the genital organs of both sexes. They also occur in connection with the nerves of the joints and in some other situations, as in the mesentery and pancreas of the cat and along the tibia of the rabbit. Each of these corpuscles is attached to and encloses the termination of a single nerve fiber. The corpuscle, which is perfectly visible to the naked eye and which can be most easily demonstrated in the mesentery of a cat, consists of a number of lamella or capsules arranged more or less concentrically around a central clear space in which the nerve fiber is contained. Each lamella is composed of bundles of fine connective tissue fibers and is lined on its inner surface by a single layer of flattened epithelioid cells. The center clear space, which is elongated or cylindrical in shape, is filled with a transparent core, in the middle of which the axis cylinder transverses the space to near its distal extremity, where it ends in one or more small knobs. Todd and Bowman have described minute arteries as entering by the sides of the nerves and forming capillary loops in the intercapsular spaces and even penetrating into the central space. Herbst has described a nerve ending somewhat similar to the Pacinian corpuscle in the mucous membrane of the tongue of the duck and in some other situations. It differs, however, from the Pacinian corpuscle in being smaller, in its capsules being more closely approximated, and especially in the act that the axis cylinder in the central clear space is coated with a continuous row of nuclei. These bodies are known as the corpuscles of Herbst. The corpuscles of Golgi and Mizoni are found in the subcutaneous tissue of the pulp of the fingers. They differ from Pacinian corpuscles in that their capsules are thinner, their contained core is thicker, and in the latter the axis cylinders ramify more extensively and end in flat expansions. The tactile corpuscles of Wagner and Meisner are oval-shaped bodies. Each is enveloped by a connective tissue capsule, and imperfect membranous septa derived from this penetrate the interior. The axis cylinder passes through the capsule, and after making several spiral turns around the body of the corpuscle ends in small globular or pyrofoam enlargements. These tactile corpuscles occur in the papillae of the corium of the hand and foot, the front of the forearm, the skin of the lips, the mucus membrane of the tip of the tongue, the palpable conjunctiva, and the skin of the mammary papilla. Corpuscles of Rafini Rafini described a special variety of nerve endings in the subcutaneous tissue of the human finger. They are principally situated at the junction of the corium with the subcutaneous tissue. They are oval in shape and consist of strong connective tissue sheaths, inside which the nerve fibers divide into numerous branches, which show varicocities and end in small free knobs. The neurotendinous spindles, organs of Golgi, are chiefly found near the junctions of tendons and muscles. Each is enclosed in a capsule which contains a number of enlarge tendon fasciculi, intrafusal fasciculi. One or more nerve fibers perforate the side of the capsule and lose their medullary sheaths. The axis cylinders subdivide and end between the tendon fibers and irregular discs or varicocities. The neuromuscular spindles are present in the majority of voluntary muscles and consist of small bundles of particular muscular fibers, intrafusal fibers. Embryonic in type, invested by capsules, within which nerve fibers, experimentally shown to be sensory in origin, terminate. These neuromuscular spindles vary in length from 0.8 mm to 5 mm and have a distinctly fusiform appearance. The large medallated nerve fibers passing to the end organ are from 1 to 3 or 4 in number. Entering the fibers capsule, they divide several times and, losing their medullary sheaths, ultimately end in naked axis cylinders and circling the intrafusal fibers to flattened expansions or irregular ovoid or rounded discs. Neuromuscular spindles have not yet been demonstrated in the tongue muscles and only a few exist in the ocular muscles. End of section 61, recording by David Lawrence in Brampton, Ontario, September 2009. Section 62 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. Recorded by Larianne Walden. Anatomy of the Human Body, Part 4 by Henry Gray. The Common Integument, Part 1. Integumentum commune, Skin. The integument covers the body and protects the deeper tissues from injury, from drying, and from invasion by foreign organisms. It contains the peripheral endings of many of the sensory nerves. It plays an important part in the regulation of the body temperature and has also limited excretory and absorbing powers. It consists principally of a layer of vascular connective tissue named the corium or cutis vira and an external covering of epithelium, termed the epidermis or cuticle. On the surface of the former layer are sensitive and vascular papillae. Within or beneath it are certain organs with special functions, namely the pseudoriferous and sebaceous glands and the hair follicles. The epidermis, cuticle, or scarf skin is non-vascular and consists of stratified epithelium and is accurately molded on the papillary layer of the corium. It varies in thickness in different parts. In some situations, as in the palms of the hands and soles of the feet, it is thick, hard, and horny in texture. This may be in a measure due to the fact that these parts are exposed to intermittent pressure, but that this is not the only cause is proved by the fact that the condition exists to a very considerable extent at birth. The more superficial layers of cells, called the horny layer, stratum corneum, may be separated by maceration from a deeper stratum, which is called the stratum mucosum, and which consists of several layers of differently shaped cells. The free surface of the epidermis is marked by a network of linear furrows of variable size, dividing the surface into a number of polygonal or lozenge shaped areas. Some of these furrows are large, as opposite the flexures of the joints, and correspond to the folds in the corium produced by movements. In other situations, as upon the back of the hand, they are exceedingly fine and intersect one another at various angles. Upon the palmar surfaces of the hands and fingers, and upon the soles of the feet, the epidermal ridges are very distinct and are disposed in curves. They depend upon the large size and peculiar arrangements of the papillae, upon which the epidermis is placed. The function of these ridges is primarily to increase resistance between contact surfaces for the purpose of preventing slipping, whether in walking or prehension. The direction of the ridges is at right angles with the force that tends to produce slipping, or to the resultant of such forces, when these forces vary in direction. Footnote. Professor Arthur Thompson of Oxford suggests that the contraction of these muscles on follicles which contain weak, flat hairs will tend to produce a permanent curve in the follicle, and this curve will be impressed on the hair which is molded within it, so that the hair on emerging through the skin will be curled. Curved hair follicles are characteristic of the scalp of the bushman. End footnote. In each individual, the lines on the tips of the fingers and thumbs form distinct patterns unlike those of any other person. A method of determining the identity of a criminal is based on this fact. Impressions, fingerprints of these lines being made on paper covered with soot or on white paper after first covering the fingers with ink. The deep surface of the epidermis is accurately molded upon the papillary layer of the corium, the papillary being covered by a basement membrane, so that when the epidermis is removed by maceration, it presents on its undersurface a number of pits or depressions corresponding to the papillary, and ridges corresponding to the intervals between them. Fine tubular prolongations are continued from this layer into the ducts of the pseudoriferous and sebaceous glands. The epidermis consists of stratified epithelium which is arranged in four layers from within outward as follows. A. stratum mucosum, B. stratum granulosum, C. stratum lucidum, and D. stratum corneum. The stratum mucosum mucous layer is composed of several layers of cells. Those of the deepest layer are columnar in shape and placed perpendicularly on the surface of the basement membrane, since they are attached by toothed extremities. This deepest layer is sometimes termed the stratum germinativum. The succeeding strata consists of cells of a more rounded or polyhedral form, the contents of which are soft, opaque, granular, and soluble in acetic acid. These are known as prickle cells because of the bridges by which they are connected to one another. They contain fine fibrils which are continuous across the connecting processes with corresponding fibrils in adjacent cells. Between the bridges are fine intercellular clefts serving for the passage of length, and in these, lymph corpuscles or pigment granules may be found. The stratum granulosum comprises two or three layers of flattened cells which contain granules of alidin, a substance readily stained by hematoxilin or carmin, and probably an intermediate substance in the formation of keratin. They are supposed to be cells in a transitional stage between the protoplasmic cells of the stratum mucosum and the horny cells of the superficial layers. The stratum lucidum appears in section as a homogenous or dimly striated membrane composed of closely packed cells in which traces of flattened nuclei may be found and in which minute granules of a substance named keratohylin are present. The stratum corneum, horny layer, consists of several layers of horny epithelial scales in which no nuclei are discernible and which are unaffected by acetic acid, the protoplasm having become changed into horny material or keratin. According to Ranvier they contain granules of a material which has the characteristics of beeswax. The black color of the skin in the negro and the tawny color among some of the white races is due to the presence of pigment in the cells of the epidermis. This pigment is more especially distinct in the cells of the stratum mucosum and is similar to that found in the cells of the pigmentary layer of the retina. As the cells approach the surface and desiccate the color becomes partially lost. The disappearance of the pigment from the superficial layers of the epidermis is, however, difficult to explain. The pigment, melanin, consists of dark brown or black granules of very small size closely packed together within the cells but not involving the nucleus. The main purpose served by the epidermis is that of protection. As the surface is worn away new cells are supplied and thus the true skin, the vessels and nerves which it contains are defended from damage. The corium, cutisfera, dermis or true skin is tough, flexible and highly elastic. It varies in thickness in different parts of the body. Thus it is very thick in the palms of the hand and soles of the feet. Thicker on the posterior aspect of the body than on the front and on the lateral than on the medial sides of the limbs. In eyelid, scrotum and penis it is exceedingly thin and delicate. It consists of felted connective tissue with a varying amount of elastic fibers and numerous blood vessels, lymphatics and nerves. The connective tissue is arranged in two layers, a deeper or reticular and a superficial or papillary. Unstriped muscular fibers are found in the superficial layers of the corium wherever hairs are present and in the subcutaneous areolar tissue of the scrotum, penis, labia majora and nipples. In the nipples the fibers are disposed in bands, closely reticulated and arranged in superimposed lamini. The reticular layer, stratum reticulari, deep layer, consists of strong interlacing bands composed chiefly of white fibrous tissue but containing some fibers of yellow elastic tissue which vary in number in different parts and connective tissue corpuscles which are often to be found flattened against the white fibrous tissue bundles. Toward the attached surface the fasciculi are large in course and the areole left by their interlacement are large and occupied by adipose tissue and sweat glands. Below the reticular layer is the subcutaneous areolar tissue which except in a few situations contains fat. The papillary layer, stratum papillary, superficial layer, corpus papillary of the corium consists of numerous small highly sensitive and vascular immanences, the papilly which rise perpendicularly from its surface. The papilly are minute conical immanences having rounded or blunted extremities occasionally divided into two or more parts and are received into corresponding pits on the under surface of the cuticle. On the general surface of the body, more especially in parts endowed with slight sensibility they are few in number and exceedingly minute. But in some situations as upon the palmar surfaces of the hands and fingers and upon the plantar surfaces of the feet and toes they are long of large size closely aggregated together and arranged in parallel curved lines forming the elevated ridges seen on the free surface of the epidermis. Each ridge contains two rows of papilly between which the ducts of the pseudoriferous glands pass outward to open on the summit of the ridge. Each papilla consists of very small and closely interlacing bundles of finely fibrillated tissue with a few elastic fibers. Within this tissue is a capillary loop and in some papilly, especially in the palms of the hands and fingers there are tactile corpuscles. Development The epidermis and its appendages consisting of the hairs, nails, sebaceous and sweat glands are developed from the ectoderm while the corium or true skin is of mesodermal origin. About the fifth week the epidermis consists of two layers of cells the deeper one corresponding to the reed mucosum. The subcutaneous fad appears about the fourth month and the papilly of the true skin about the sixth. A considerable desquamation of epidermis takes place during fetal life and this desquamated epidermis mixed with sebaceous secretion constitutes the vernix caseosa with which the skin is smeared during the last three months of fetal life. The nails are formed at the third month and begin to project from the epidermis about the sixth. The hairs appear between the third and fourth months in the form of solid down growths of the deeper layer of the epidermis the growing extremities of which become inverted by papillary projections and the corium. The central cells of the solid down growths undergo alteration to form the hair while the peripheral cells are retained to form the lining cells of the hair follicle. About the fifth month the fetal hairs lanugo appear first on the head and then on the other parts they drop off after birth and give place to the permanent hairs. The cellular structures of the pseudoriferous and sebaceous glands are formed from the ectoderm while the connective tissue and blood vessels are derived from the mesoderm. All the sweat glands are fully formed at birth they begin to develop as early as the fourth month. The artery supplying the skin form a network in the subcutaneous tissue and from this network branches are given off to supply the pseudoriferous glands, the hair follicles and the fat. Other branches unite in a plexus immediately beneath the corium. From this plexus fine capillary vessels pass into the papillae forming in the smaller ones a single capillary loop but in the larger a more or less convoluted vessel. The lymphatic vessels of the skin form two networks superficial and deep which communicate with each other and with those of the subcutaneous tissue by oblique branches. The nerves of the skin terminate partly in the epidermis and partly in the corium. Their different modes of ending are described on pages 1059 to 1061. End of section 62. Section 63 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. Recorded by Larianne Walden. Anatomy of the Human Body Part 4 by Henry Gray. The Common Integument Part 2. The Appendages of the Skin. The appendages of the skin are the nails, the hairs and the pseudoriferous and sebaceous glands with their ducts. The nails, unguys, are flattened elastic structures of a horny texture placed upon the dorsal surfaces of the terminal phalanges of the fingers and toes. Each nail is convex on its outer surface, concave within and is implanted by a portion called the root into a groove in the skin. The exposed portion is called the body and the distal extremity, the free edge. The nail is firmly adherent to the corium being accurately molded upon its surface. The part beneath the body and root of the nail is called the nail matrix because from it the nail is produced. Under the greater part of the body of the nail the matrix is thick and raised into a series of longitudinal ridges which are very vascular and the color is seen through the transparent tissue. Near the root of the nail the papillae are smaller, less vascular and have no regular arrangement and here the tissue of the nail is not firmly adherent to the connective tissue stratum but only in contact with it. Hence this portion is of a whiter color and is called the lunula on account of its shape. The cuticle as it passes forward on the dorsal surface of the finger or toe is attached to the surface of the nail a little in advance of its root. At the extremity of the finger it is connected with the under surface of the nail a little behind its free edge. The cuticle and the horny substance of the nail, both epidermic structures, are thus directly continuous with each other. The superficial horny part of the nail consists of a greatly thickened stratum lucidum, the stratum corium forming merely the thin, cuticular fold eponychium that overlaps the lunula. The deeper part consists of the stratum mucosum. The cells in contact with the papillae of the matrix are columnar in form and arranged perpendicularly to the surface. Those which succeed them are of a rounded or polygonal form, the more superficial ones becoming broad, thin and flattened and so closely packed as to make the limits of the cells very indistinct. The nails grow in length by the proliferation of the cells of the stratum mucosum and in thickness from that part of the stratum mucosum which underlies the lunula. Hairs, pilae, are found on nearly every part of the surface of the body but are absent from the palms of the hands, the soles of the feet, the dorsal surfaces of the terminal phalanges, the glands penis, the inner surface of the pre-puse and the inner surfaces of the labia. They vary much in length, thickness and color in different parts of the body and in different races of mankind. In some parts, as in the skin of the eyelids, they are so short as not to project beyond the follicles containing them. In others, as upon the scalp, they are of considerable length. Again in other parts as the eyelashes, the hairs of the pubic region and the whiskers and beard, they are remarkable for their thickness. Straight hairs are stronger than curly hairs and present on transverse section a cylindrical or oval outline. Curly hairs, on the other hand, are flattened. A hair consists of a root, the part implanted in the skin and a shaft or scapus, the portion projecting from the surface. The root of the hair, radix pilae, ends in an enlargement, the hair bulb, which is whiter in color and softer in texture than the shaft and is lodged in a follicular involution of the epidermis called the hair follicle. When the hair is of considerable length, the follicle extends into the subcutaneous cellular tissue. The hair follicle commences on the surface of the skin with a funnel-shaped opening and passes inward in an oblique or curved direction, the latter in curly hairs, to become dilated at its deep extremity where it corresponds with the hair bulb. Opening into the follicle, near its free extremity, are the ducts of one or more sebaceous glands. At the bottom of each hair follicle is a small, conical, vascular eminence or papilla, similar in every respect to those found upon the surface of the skin. It is continuous with the dermic layer of the follicle and is supplied with nerve fibrils. The hair follicle consists of two coats, an outer or dermic and an inner or epidermic. The outer or dermic coat is formed mainly of fibrous tissue. It is continuous with the corium, is highly vascular, and supplied by numerous minute nervous filaments. It consists of three layers. The most internal is a hyalin basement membrane, which is well marked in the larger hair follicles, but is not very distinct in the follicles of minute hairs. It is limited to the deeper part of the follicle. Outside this is a compact layer of fibrous and spindle-shaped cells arranged circularly around the follicle. This layer extends from the bottom of the follicle as high as the entrance of the ducts of the sebaceous glands. Externally is a thick layer of connective tissue arranged in longitudinal bundles, forming a more open texture and corresponding to the reticular part of the corium. And this are contained the blood vessels and nerves. The inner or epidermic coat is closely adherent to the root of the hair and consists of two strata named respectively, the outer and the subcutaneous. The strata named respectively, the outer and inner root sheaths. The former of these corresponds with the stratum mucosum of the epidermis and resembles it in the rounded form and soft character of its cells. At the bottom of the hair follicle these cells become continuous with those of the root of the hair. The inner root sheath consists of, one, a delicate cuticle next to the hair composed of a single layer of implicated scales with atrophied nuclei. Two. One or two layers of horny, flattened, nucleated cells known as Huxley's layer. And three. A single layer of cubicle cells with clear flattened nuclei called Henley's layer. The hair bulb is molded over the papilla and composed of polyhedral epithelial cells which as they pass upward into the root of the hair become elongated and spindle shaped except some in the center which remain polyhedral. Some of these ladder cells contain pigment granules which give rise to the color of the hair. It occasionally happens that these pigment granules completely fill the cells in the center of the bulb. This gives rise to the dark tract of pigment often found of greater or less length and the axis of the hair. The shaft of the hair, scapus pilli, consists from within outward of three parts the medulla, the cortex and the cuticle. The medulla is usually wanting in the fine hairs covering the surface of the body and commonly in those of the head. It is more opaque and deeper colored than the cortex when viewed by transmitted light but when viewed by reflected light it is white. It is composed of rows of polyhedral cells containing granules of a lidon and frequently air spaces. The cortex constitutes the chief part of the shaft. Its cells are elongated and united to form flattened fusiform fibers which contain pigment granules in dark hair and air in white hair. The cuticle consists of a single layer of flat scales which overlap one another from below upward. Connected with the hair follicles are minute bundles of involuntary muscular fibers termed the eryctories pilorum. They arise from the superficial layer of the corium and are inserted into the hair follicle below the entrance of the duct of the gland. They are placed on the side toward which the hair slopes and by their action diminish the obliquity of the follicle and elevate the hair. The sebaceous gland is situated in the angle which the erector muscle forms with the superficial portion of the hair follicle and contraction of the muscle thus tends to squeeze the sebaceous secretion out from the duct of the gland. The sebaceous glands, glandular sebaceae are small, saculated, glandular organs lodged in the substance of the corium. They are found in most parts of the skin but are especially abundant in the scalp and face. They are also very numerous around the apertures of the anus, nose, mouth and external ear but are wanting in the palms of the hands and soles of the feet. Each gland consists of a single duct more or less capacious which emerges from a cluster of oval or flask shaped alveoli to five in number but in some instances there may be as many as twenty. Each alveolus is composed of a transparent basement membrane enclosing a number of epithelial cells. The outer or marginal cells are small and polyhedral and are continuous with the cells lining the duct. The remainder of the alveolus is filled with larger cells containing fat except in the center where the cells have become broken up leaving a cavity filled with their debris in any matter which constitutes the sebum cutanium. The ducts open most frequently into the hair follicles but occasionally upon the general surface as in the labia minora and the free margin of the lips. On the nose and face the glands are of large size distinctly lobulated and often become much enlarged from the accumulation of pent up secretion. The tarsal glands of the eyelids are elongated sebaceous glands with numerous lateral diverticula. The pseudoriferous or sweat glands glandular pseudoriphery are found in almost every part of the skin and are situated in small pits on the under surface of the corium or more frequently in the subcutaneous areolar tissue surrounded by a quantity of adipose tissue. Each consists of a single tube the deep part of which is rolled into an oval or spherical ball named the body of the gland while the superficial part or duct traverses the corium and cuticle and opens on the surface of the skin by a funnel shaped aperture. In the superficial layers of the corium the duct is straight but in the deeper layers it is convoluted or even twisted. Where the epidermis is thick as in the palms of the hand and soles of the feet the part of the duct which passes through it is spirally coiled. The size of the glands varies they are especially large in the regions where the amount of perspiration is great as in the axillae where they form a thin, mammalated layer of a reddish color which corresponds exactly to the situation of the hair in this region they are large also in the groin their number varies they are very plentiful on the palms of the hands and on the soles of the feet where the orifices of the ducts are exceedingly regular and open on the curved ridges they are least numerous and there are about 370 per square centimeter on the back of the hand about 200 forehead, 175 breast, abdomen and forearm 155 and on the leg and back from 60 to 80 per square centimeter Krause estimates the total number at about 2 million the average number of sweat glands per square centimeter of skin area in various races as shown by the fingers is as follows 558.2 American Negro 597.2 Filipino 653.6 Moro 684.4 Negrito Adult 709.2 Hindu 738.2 Negrito Youth 950 they are absent in the deeper portion of the external auditory meatus the prepuse and the gland's penis the tube both in the body of the gland and in the duct consists of two layers an outer of fine areolar tissue and an inner of epithelium the outer layer is thin and is continuous with the superficial stratum of the corium in the body of the gland the epithelium consists of a single layer of cubicle cells between the deep ends of which and the basement membrane are striped muscular fibers the ducts are destitute of muscular fibers and are composed of a basement membrane lined by two or three layers of polyhedral cells the lumen of the duct is coated by a thin cuticle when the cuticle is carefully removed from the surface of the corium the ducts may be drawn out in the form of short thread-like processes on its under surface the seruminous glands of the external acoustic meatus and the region of the eyelids are modified pseudoriferous glands End of Section 63 End of Anatomy of the Human Body Part 4 by Henry Gray