 Section 18 of Gray's Anatomy, Part 1. Ribs are elastic arches of bone, which form a large part of the thoracic skeleton. They are twelve in number on either side, but this number may be increased by the development of a cervical or lumbar rib, or may be diminished to eleven. The first seven are connected behind with a vertebral column, and in front, through the intervention of the costal cartilages with the sternum. They are called two or vertebro sternal ribs, footnote. Sometimes the eighth rib cartilage articulates with the sternum. This condition occurs more frequently on the right than on the left side, and footnote. The remaining five are false ribs. Of these, the first three have the cartilages attached to the cartilage of the rib above, vertebro chondral. The last two are free at their interior extremities and are termed floating or vertebral ribs. The ribs vary in their direction, the upper ones being less oblique than the lower. The obliquity reaches its maximum at the ninth rib and gradually decreases from that rib to the twelfth. The ribs are situated one below the other in such a manner that spaces called intercostal spaces are left between them. The length of each space corresponds to that of the adjacent ribs and the cartilages. The breadth is greater in front than behind, and between the upper and the lower ribs. The ribs increase in length from the first to the seventh below, which they diminish to the twelfth. In breadth, they decrease from above downward, and in the upper ten, the greatest breadth is at the external extremity. Common characteristics of the ribs A rib in the middle of the series should be taken in order to study the common characteristics of these bones. Each rib has two extremities, a posterior or vertebral and an anterior or sternal, and an intervening portion, the body or shaft. Posterior extremity The posterior or vertebral extremity presents, for examination, a head, neck, and tubercle. The head is marked by a kidney-shaped articular surface, divided by a horizontal crest into two facets for articulation, with the depression formed on the bodies of two adjacent thoracic vertebrae. The upper facet is a smaller, till the crest is attached with the interarticular ligament. The neck is a flattened portion, which extends lateralward from the head. It is about 2.5 centimeters long, and is placed in front of the transverse process of the lower of the two vertebrae, with which the head articulates. Its anterior surface is flat and smooth, its posterior rough for the attachment of the ligament of the neck, and perforated by numerous forearmina. Of its two borders, the superior presents a rough crest, crista coli costo, for the attachment of the anterior costo transverse ligament. Its inferior border is rounded. On the posterior surface, at the juncture of the neck and body, the nearer the lower, then the upper border, is an eminence, the tubercle. It consists of an articular and non-articular portion. The articular portion, the lower and more medial of the two, presents a small oval surface for articulation, with the end of the transverse process of the lower of the two vertebrae, to which the head is connected. The non-articular portion is a rough elevation, and affords attachment to the ligament of the tubercle. The tubercle is much more prominent in the upper than in the lower ribs. BODY The body or shaft is thin and flat, with two surfaces, an external and an internal, and two borders, a superior and an inferior. The external surface is convex, smooth and marked, a little in front of the tubercle, by a prominent line. Directed downward and lateralward, this gives attachment to a tendon of the iliocostellus, and is called the angle. At this point, the rib is bent in two directions, and at the same time twisted on its long axis. If the rib be laid upon its lower border, the portion of the body in front of the angle rests upon this border, while the portion behind the angle is bent medialward, and at the same time tilted upward, as the result of the twisting, the external surface, behind the angle, looks downward, and in front of the angle, slightly upward. The distance between the angle and the tubercle is progressively greater for the second to the tenth ribs. The portion between the angle and the tubercle is rounded, rough and irregular, and serves for the attachment of the lungesumis dorsi. The internal surface is concave, smooth, directed a little upward, behind the angle, a little downward in front of it, and is marked by a ridge which commences at the lower extremity of the head. This ridge is strongly marked as far as the angle, and gradually becomes lost at the junction of the anterior and middle thirds of the bone. Between it and the inferior border is a groove, a costal groove, for the intercostal vessels and nerve. At the back part of the bone, this groove belongs to the inferior border, but just in front of the angle, where it is deepest and broadest, it is on the internal surface. The superior edge of the groove is rounded, and serves for the attachment of an intercostalus internus. The inferior edge corresponds to the lower margin of the rib, and gives attachment to an intercostalus externus. Within the groove are seen the orifices of numerous small four amina for nutrient vessels which traverse the shaft obliquely from the Bifflemore backward. The superior border, thick and rounded, is marked by an external and an internal lip. More distinct, behind, than in front, would serve for the attachment of intercostalus externus and internus. The inferior border is thin, and has attach to it an intercostalus externus. Anterior extremity. The anterior, or external extremity, is flattened, and presents a porous, oval, concave depression into which the costal cartilage is received. Peculiar Ribs. The first, second, tenth, eleventh, and twelfth ribs present certain variations from the common characteristics described above, and require a special consideration. First Rib. The first rib is the most curved, and usually the shortest of all the ribs. It is broad and flat. It surfaces looking upward and downward, and its borders inward and outward. The head is small, rounded, and possesses only a single articular facet, for articulation with the body of the first thoracic vertebra. The neck is narrow and rounded. The tubercle, thick and prominent, is placed on the outer border. There is no angle, but at the tubercle, the rib is slightly bent, with its convexity upward, so that the head of the bone is directed downward. The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle. The scalene tubercle, for the attachment of the scaliness anterior, the anterior groove transmit the subclavian vein. The posterior and subclavian artery, and the lowest trunk of the brachial plexus. Behind the posterior groove is a rough area for the attachment of the scalene dismedius. The undersurfaces smooth and destitute of a costal groove. The outer border is convex, thick, and rounded, and at its posterior part gives attachment to the first digitization of the serratus anterior. The inner border is concave, thin, and sharp, and marked about at center by the scalene tubercle. The anterior extremity is larger and thicker than that of any of the other ribs. The second rib. The second rib is much longer than the first, but has a very similar curvature. The non-articular portion of the tubercle is occasionally only feebly marked. The angle is slight and situated close to the tubercle. The body is not twisted, so that both ends touch any plain surface upon which it may be laid, but there is a bend with its convexity upward, similar to, though smaller than, that found in the first rib. The body is not flattened horizontally like that of the first rib. Its external surface is convex and looks upward and a little outward. Near the middle of it is a rough eminence for the origin of the lower part of the first and the hole of the second digitation of the serratus anterior. Behind and above, this is attached to the scaleness posterior. The internal surface, smooth and concave, is directed downward and a little inward. On its posterior part, there is a short costal groove. Tenth rib. The tenth rib has only a single articular facet on its head. Eleventh and twelfth ribs. The eleventh and twelfth ribs have each a single articular facet on the head, which is a rather large size. They have no necks or tubercles that are pointed at their anterior ends. The eleventh has a slight angle and a shallow costal groove. The twelfth is neither. It is much shorter than the eleventh, and its head is inclined slightly downward. Sometimes the twelfth rib is even shorter than the first. Structure. The ribs consist of highly vascular, cancellous tissue enclosed in a thin layer of compact bone. Osification. Each rib, with the exception of the last two, is ossified from four centers, primary center for the body, and three epiphyseal centers. One for the head and one each for the articular and nonarticular parts of the tubercle. The eleventh and twelfth ribs have each only two centers. Those for the tubercle's being wanting. Osification begins near the angle toward the end of the second month of fetal life, and is seen first in the sixth and seventh ribs. The epiphysis for the head and tubercle make their appearance between the 16th and 20th years, and are united to the body about the 25th year. Facet states that in all probability there is usually no epiphysis on the nonarticular part of the tuberosity below the sixth or seventh rib. End of section 18. Recording by Jennifer Stearns, Concord, New Hampshire. Section 19 of Grays Anatomy Part 1. 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 Jennifer Stearns. Anatomy of the Human Body Part 1 by Henry Gray. Section 19, The Costal Cardilages. Cardilagines costalis. The Costal Cardilages are bars of hyaline cartilage which serve to prolong the ribs forward and contribute very materially to the elasticity of the walls of the thorax. The first seven pairs are connected with the sternum. The next three are each articulated with a lower border of the cartilage of the preceding rib. The last two have pointed extremities, which end in the wall of the abdomen. Like the ribs, the Costal Cardilages vary in their length, breadth, and direction. They increase in length from the first seventh, then gradually decrease to the twelfth. Their breadth, as well as that of the intervals between them, diminishes from the first to the last. They are broad of their attachments to the ribs and taper toward their sternal extremities, accepting the first two, which are of the same breadth throughout, and the sixth, seventh, and eighth, which are enlarged where the margins are in contact. They also vary in direction. The first descends a little. The second is horizontal. The third ascends slightly, while the others are angular, following the course of the ribs for a short distance and then ascending to the sternum or preceding cartilage. Each Costal Cartilage presents two surfaces, two borders, and two extremities. Surfaces. The anterior surface is convex and looks forward and upward. That of the first gives attachment to the Costal Clavicular ligament and the Subclavius muscle. Those of the first six or seven at their sternal ends to the pectoralis major. The others are covered by and give partial attachment to some of the flat muscles of the abdomen. The posterior surface is concave and directed backward and downward. That of the first gives attachment to the sternothyroidus. Those of the third to the sixth inclusive of the transversus thoracis and the six or seven inferior ones to the transversus abdominis and the diaphragm. Borders. Of the two borders, the superior is concave. The inferior convex. They afford attachment to the intercostalus internii. The upper border of the six gives attachment also to the pectoralis major. The inferior borders of the six, seventh, eighth, and ninth cartilages present heel-like projections at the points of greatest convexity. These projections carry smooth oblong facets which articulate respectively with facets and slight projections from the upper borders of the seventh, eighth, ninth, and tenth cartilages. Extravities. The lateral end of each cartilage is continuous with the osseous tissue of the rib to which it belongs. The medial end of the first is continuous with the sternum. The medial ends of the sixth, succeeding ones are rounded and are received into shallow concavities on the lateral martens of the sternum. The medial ends of the eighth, ninth, and tenth costal cartilages are pointed and are connected each with a cartilage immediately above. Those of the 11th and 12th are pointed and free. In old age, the costal cartilages are prone to undergo superficial ossification. Cervical ribs, derived from the seventh cervical vertebra, are of not infrequent occurrence and are important clinically because they may give rise to obscured nervous or vascular symptoms. The cervical rib may be a mere apophysis, articulating only with the transverse process of the vertebra, but more commonly, it consists of a defined head, neck, and tubercle with or without a body. It extends lateralward or forward and lateralward into the posterior triangle of the neck where it may terminate in a free end or may join the first thoracic rib, the first costal cartilage or the sternum. It varies much in shape, size, direction, and mobility. If it reach far enough forward, part of the brachyloplexus in the subclavian artery and vein cross over it and our app to suffer compression and so doing. Pressure on the artery may obstruct the circulation so much that arterial thrombosis results, causing gangring of the fingertips. Pressure on the nerves is commoner and affects the eighth cervical and first thoracic nerves causing paralysis of the muscles they supply and neurologic pain and paracetia in the area of skin to which they are distributed. No ocular pupillary changes are to be found. The thorax is frequently found to be altered in shape in certain diseases. In rickets, the ends of the ribs where they join the costal cartilages become enlarged giving rise to the so-called rickety rosary which in mild cases is only found on the internal surface of the thorax. Lateral to these enlargements, the soften ribs sink in so as to present a groove passing downward and lateralward on either side of the sturdum. This bone is forced forward by the bending of the ribs and the anterior and the anterior posterior diameter of the chest is increased. The ribs affected of the second to the eighth, the lower ones being prevented from falling in by the presence of the liver, stomach, and spleen and when the abdomen is distended as it often is in rickets, the lower ribs may be pushed outward causing a transverse groove. Harrison sulcus, just above the costal arch. This deformity or forward projection of the sturdum often asymmetrical is known as pigeon breast and may be taken as evidence of active or old rickets except in cases of primary spinal curvature. In many instances, it is associated in children with obstruction in the upper air passages due to enlarge tonsils or adenoid growths. In some rickety children or adults and also in others who give no history or further evidence of having had rickets, an opposite condition obtains. The lower part of the sturdum and often the cyphoid process as well are deeply depressed backward producing an oval hollow in the lower sternal and upper epigastric regions. This is known as funnel breast. German trick or boost. It never appears to reduce the least disturbance of any of the vital functions. The physical chest is often long and narrow and with great obliquity of the ribs and projection of the scapulae. In pulmonary emphysema, the chest is enlarge in all its diameters and presents on section an almost circular outline. It has received the name of the barrel shaped chest. In severe cases of lateral curvature of the vertebral column, the thorax becomes much distorted. In consequence of the rotation of the bodies of the vertebra, which takes place in this disease, the ribs opposite the convexity of the dorsal curve become extremely convex behind, being thrown out and bulging and at the same time flattened in front so that the two ends of the same rib are almost parallel. Coincidentally, with this the ribs on the opposite side on the concavity of the curve are sunk and depressed behind and bulging and convex in front. End of section 19. Recording by Jennifer Stearns, Concord, New Hampshire. Section 20 of Gray's Anatomy Part 1. 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 Jennifer Stearns. Anatomy of the Human Body Part 1 by Henry Gray. Section 20, the skull. The skull is supported on the summit of the vertebral column and is of an oval shape, wider behind than in front. It is composed of a series of flattened or irregular bones, which, with one exception, the mandible, are immovably jointed together. It is divisible into two parts. One, the cranium, which lodges and protects the brain, consists of eight bones, and two, the skeleton of the face of 14, as follows. Skull, 22 bones. Cranium, eight bones. Hospital, two parietals. Frontal, two temporals. Sphenoidal, ethmoidal. Face, 14 bones. Two nasals, two maxillae. Two lacrimals. Two zygomatics. Two palatines. Two inferior nasal concave. Vulmar, mandible. In the basal nomenclature, certain bones developed in association with the nasal capsule, the inferior nasal concave, the lacrimals, the nasals, and the vulmar, are grouped as cranial and not as facial bones. The hyoid bone, situated at the root of the tongue and attached to the base of the skull by ligaments, is described in the section. The occipitobone. Osocranium. And occipitalae. The occipitobone, situated at the back and lower part of the cranium, is trapezoid in shape and curved on itself. It is pierced by a large oval aperture, the foremen magnum, through which the cranial cavity communicates with a vertebral canal. The curved, expanded plate behind the foremen magnum, is named the squama. The thick, somewhat quadrilateral piece in front of the foremen is called the basilar part. Waltzed on either side of the foremen is the lateral portion. The squama. Squama aspartalis. The squama, situated above and behind the foremen magnum, is curved from above downward and from side to side. Cercoses. The external surface is convex and presents midway between the summit of the bone and the foremen magnum, a prominence, the external occipital protuberance. Extending lateralward from this on either side are two curved lines, one a little above the other. The upper, often faintly marked, is named the highest neutral line. And to it, the galea aponeurotica is attached. The lower is termed the superior neutral line. That part of the squama, which lies above the highest neutral lines, is named the planum occipitali, and is covered by the occipitalis muscle. That below, termed the planum occipitali, is rough and irregular for the attachment of several muscles. From the external occipital protuberance, a ridge or crest, the median neutral line, often faintly marked, descends to the foremen magnum and affords attachment to the ligamentum nuce. Running from the middle of this line across either half of the neutral plane is the inferior neutral line. Several muscles are attached to the outer surface of the squama. Thus, the superior neutral line gives origin to the occipitalis trapezius, and insertion to the sternocleidomastiotis and splenius capitis. Into the surface between the superior and inferior neutral lines, semi-spinalis capitis, and the obliquus capitis superior are inserted. Of the inferior neutral line and the area below it, receive the insertions of the recti-capitis posterioris major and minor. The posterior atlantiooccipital membrane is attached around the posterior lateral part of the foremen magnum, just outside the margin of the foremen. The internal surface is deeply concave and divided into four fossae, cusciate eminence. The upper two fossae are triangular and lodge the occipital bones of the cerebrum to lower to a quadrilateral and accommodate the hemispheres of the cerebellum. At the point of intersection of the four divisions of the cusciate eminence is the internal occipital protuberance. From this protuberance, the upper division of the cusciate eminence runs to the superior angle of the bone and on one side of it, generally the right, is a deep groove, the sagittal sulcus, which lodges the hinder part of the superior sagittal sinus. To the margins of the sulcus, the fax cerebrum is attached. The lower division of the cusciate eminence is prominent and is named the internal occipital crest. It befercates the other form in magnum and gives attachment to the fox cerebelli. Then the attached margin of the fox is the occipital sinus, which is sometimes duplicated. In the upper part of the internal occipital crest, a small depression is sometimes distinguishable. It is termed the ferrimin fossa since it is occupied by part of the vermus of the cerebellum. Transverse grooves, one on either side, extend from the internal occipital protuberance to the lateral angles of the bone. Those grooves accommodate the transverse sinuses and their prominent margins give attachment to the tentorium cerebelli. The groove on the right side is usually larger than that on the left and is continuous with that for the superior sagittal sinus, exceptions to this condition are, however, not infrequent. The left may be larger than the right or the tube may be almost equal in size. The angle of union of the superior sagittal and transverse sinuses is named the confluence of the sinuses. The columns of blood coming in different directions were supposed to be pressed together at this point, particular a wine press and footnote. And its position is indicated by a depression situated on one or other side of the protuberance. The lateral parts are situated at the sides of the foremen magnum. On their under surfaces are the condolese articulation with the superior facets of the atlas. The condolese are oval or retiform in shape and their interior extremities directed forward and medialward are closer together than their posterior and encroach on the basilar portion of the bone. The posterior extremities extend back to the level of the middle of the foremen magnum. The aticular surfaces of the condolese are convex from before backward and from side to side and look downward and lateralward. To their margins are attached to the capsules of the elantooccipital articulations and on the medial side of each is a rough impression or tubercle for the aller ligament. At the base of either condyle the bone is tunneled by a short canal the hypoglossal canal interior condyloid foremen. This begins on the cranial surface of the bone immediately above the foremen magnum and is directed lateralward and forward above the condyle. It may be partially or completely divided into two by a specular of bone. It gives exit to the hypoglossal or 12th cerebral nerve and entrance to a meningeal branch of the ascending pharyngeal artery. Behind either condyle is a depression the condyloid fossa which receives the posterior margin of the superior facet of the atlas when the head is bent backward. The floor of this fossa is sometimes perforated by a condyloid canal through which an emissary vein passes from the transverse sinus extending lateralward and the posterior half of the condyle as a quadrilateral plate of bone the jugular process excavated in front by the jugular notch which in the articulated skull forms a posterior part of the jugular form. The jugular notch may be divided into two by a bony specule the intra-jugular process which projects lateralward above the hypoglossal canal. The under-surface of the jugular process is rough and gives attachment to the rectus capitus lateralus muscle and the lateral palantosipital ligament from the surface in eminence the peromastoid process sometimes projects downwards and may be of sufficient length to reach and articulate with the transverse process of the atlas. Laterally the jugular process presents the rough quadrilateral or triangular area which is joined to the jugular surface of the temporal bone by a plate of cartilage after the age of 25 this plate tends to ossify. The upper surface of the lateral part presents in oval eminence the jugular tubicle which overlies the hypoglossal canal and is sometimes crossed by an oblique groove for the glossopharyngeal, vagus and accessory nerves. The upper surface of the jugular process is a deep groove which curves medialward and forward and is continuous with a jugular notch. This groove lodges the terminal part of the transverse sinus and opening into it close to the medial margin is the orifice of the conaloid canal basilar part pars basilaris The basilar part extends forward and upward from the form of magnum and presents in front an area more or less quadrilateral and outline. In the young skull this area is rough and uneven and is joined to the body of the sphenoid by a plate of cartilage By the 25th year this cartilaginous plate is ossified and the occipital and sphenoid form a continuous bone. Surfaces On a slower surface about 1cm in front of the form of magnum is the pharyngeal tubicle which gives attachment to the fibrous raffae of the pharynx. On either side of the middle line the longest capitis and rectus capitis anterior are inserted and immediately in front of the form in magnum the anterior allantooccipital membrane is attached. The upper surface presents a broad shallow groove which inclines upward and forward from the form in magnum It supports the medulla oblongata and near the margin of the form in magnum gives attachment to the membrana tectoria. On the lateral margins of the surface are faint grooves for the inferior petrol cell sinuses. Form in magnum The form in magnum is a large oval aperture with its long diameter anterior posterior It is wider behind and in front where it is encroached upon by the condibus. It transmits the medulla oblongata in its membranes the accessory nerves the vertebral arteries the anterior and posterior spinal arteries and the membrana tectoria and aller ligaments. Angles The superior angle of the occipital bone articulates the occipital angles of the parietal bones In the fetal skull corresponds in position for the posterior fontanelle The inferior angle is fused with the body of the sonoid The lateral angles are situated at the extremities of the grooves for the transverse sinuses each is received into the interval between the mastoid angle of the parietal and mastoid part of the temporal Borders The superior borders extend from the inferior to the lateral angles They are deeply serrated for articulation for the occipital borders of the parietals and formed by this union the limb doidal suture The inferior borders extend from the lateral angles to the inferior angle The upper half of each articulates of the mastoid portion of the corresponding temporal The lower half of the petrus part of the same bone is serrated from one another by the jugular process The notch on the anterior surface of which forms the posterior part of the jugular filament Structure The occipital, like the other cranial the outer and inner tables between which is the cancerous tissue or diphoid The bone is especially thick at the ridges protuberances, condyles and an anterior part of the basilar part It is thin, semi-transparent and destitute of dipoi, ossification The platinum occipitalae of the swarma is developed in membrane and may remain separate throughout life when it constitutes the inter parietal bone The rest of the bone is developed in cartilage The number of nuclei for the platinum occipitalae is usually given as 4 to appearing in the middle line about the second month and to some little distance from the middle line about the third month of fetal life The platinum occipitalae of the swarma is ossified from two centers which appear above the seventh week of fetal life and soon unite to form a single piece Union of the upper and lower portions of the swarma takes place in the third month of fetal life An occasional center, kurtry appears in the posterior margin of the form and magnum in the fifth month This forms a separate occipital sometimes double which unites with the rest of the squarma before birth Each of the lateral parts visit begins to ossify from a single center during the eighth week of fetal life The basilar portion is ossified from two centers one in front of the other These appear by the sixth week of fetal life and rapidly coalesce Maul states This form, occipitalae is ossified from two centers and the basilar portion from one About the fourth year the squarma and the two lateral portions unite and about the sixth year the bone consists of a single piece Between the eighteenth and twenty-fifth years the occipital and sphenoid become united forming a single bone End of section 20 According by Jennifer Stearns, conquered New Hampshire Section 21 of Greys Anatomy Part 1 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 Jennifer Stearns Anatomy of the Human Body Part 1 by Henry Gray The parietal bone Osperitale The parietal bones form by their union the sides and roof of the cranium Each bone is irregularly quadrilateral in form and has two surfaces four borders and four angles Surfaces The external surface is convex, smooth and marked near the center by an eminence The parietal eminence Tuber parietale Which indicates the point where ossification commenced Crossing the middle of the bone in an arched direction are two curved lines the superior and inferior temporal lines The former gives attachment to the temporal fascia and the latter indicates the upper limit of the muscular origin of the temporalis Above these lines the bone is covered by the Galea aponeurotica Below them it forms part of the temporal fascia and affords attachment to the temporalis muscle At the back part and close to the upper or sagittal border is the parietal foremen which transmit a vein to the superior sagittal sinus and sometimes a small branch of the occipital artery It is not constantly present and its size varies considerably The internal surface is concave It presents depressions corresponding to the cerebral convolutions and numerous furrows for the ramifications of the middle meningeal vessel The latter run upward and backward from the synoidal angle and from the central and posterior part of the squamous border Along the upper margin is a shallow groove Which together, with that on the opposite parietal forms a channel the sagittal sulcus for the superior sagittal sinus The edges of the sulcus affords attachment to the falx cerebri Near the groove are several depressions best marked in the skulls of old persons for the arachnoid granulations Pachyonian bodies In the groove is the internal opening of the parietal foremen when the aperture exists Borders The sagittal border, the longest and thickest is dentated and articulates with its fellow of the opposite side forming the sagittal suture The squamous border is divided into three parts Of these, the anterior is thin and pointed beveled at the expense of the outer surface and overlap by the tip of the great wing of the synoid The middle portion is arched beveled at the expense of the outer surface and overlapped by the squama of the temporal The posterior part is thick and serrated for articulation with the mastoid portion of the temporal The frontal border is deeply serrated and beveled at the expense of the outer surface above and of the inner below It articulates with the frontal bone forming one half of the coronal suture The occipital border deeply denticulated articulates with the occipital forming one half of the landoidal suture Angles The frontal angle is practically a right angle and corresponds with the point of meeting of the sagittal and coronal sutures This point is named the bregma In the fetus skull and for about a year and a half after birth this region is membranous and is called the anterior fontanelle The sphenoidal angle then an acute is received into the interval between the frontal bone and the great wing of the sphenoid Its inner surface is marked by a deep groove sometimes a canal for the anterior divisions of the middle meningeal artery The occipital angle is rounded and corresponds with the point of meeting of the sagittal and landoidal sutures A point we just termed the lambda In the fetus this part of the skull is membranous and is called the posterior fontanelle The mastoid angle is truncated It articulates with the occipital bone and with the mastoid portion of the temporal and presents on its inner surface a broad shallow groove which lodges part of the transverse sinus The point of meeting of this angle with the occipital and mastoid part of the temporal is named the asterian Ossification The parietal bone is ossified in membrane from a single center which appears at the parietal eminence about the 8th week of fetal life Ossification gradually extends in a radial manner from the center toward the margins of the bone The angles are consequently the parts last formed and it is here that the fontanelles exist Occasionally the parietal bone is divided into two parts, upper and lower by an antero-posterior suture articulations The parietal articulates with 5 bones The opposite parietal the occipital frontal temporal and sphenoid The frontal bone Oss frontally The frontal bone resembles a cockle shell in form and consists of two portions A vertical portion, the squama corresponding with the region of the forehead and an orbital or horizontal portion which enters into the formation of the roofs of the orbital and nasal cavities Squama Squama frontalis Surfaces The external surface of this portion is convex and usually exhibits the lower part of the middle line the remains of the frontal or metopic suture In infancy this suture divides the bone into two a condition which may persist throughout life On either side of this suture about 3 cm above the supra orbital margin is around an elevation The frontal eminence Tuber frontale These eminences are very in size in different individuals are occasionally unsymmetrical and are especially prominent in young skulls The surface of the bone above them is smooth and covered by the Galea aponeurotica Blow the frontal eminences and separated from them by a shallow groove are two arched elevations The superciliary arches These are prominent medially and are joined to one another by an elevation named the glabella They are larger in the male than in the female and their degree of prominence depends to some extent on the size of the frontal air sinuses Footnote Some confusion is occasioned to students commencing the study of anatomy by the name sinus having been given to two different kinds of space connected with the skull It may be as well therefore to state here The sinuses in the interior of the cranium which produce the grooves on the inner surfaces of the bones are venous channels which convey the blood from the brain while the sinuses externals of the cranial cavity the frontal, sphenoidal, ethmoidal and maxillary are hollow spaces in the bones themselves They communicate with the nasal cavities and contain air and footnote Prominent ridges are, however occasionally associated with small air sinuses Beneath each superciliary arch is a curved and prominent margin the super orbital margin which forms the upper boundary of the base of the orbit and separates the squama from the orbital portion of the bone The lateral part of this margin is sharp and prominent affording to the eye in that situation considerable protection from injury the medial part is rounded at the junction of its medial and intermediate thirds is a notch sometimes converted into a foreman the super orbital notch or foreman which transmits the super orbital vessels and nerve A small aperture in the upper part of the notch transmits a vein from the diploid to join the super orbital vein The super orbital margin ends laterally in the zygomatic process which is strong and prominent and articulates with the zygomatic bone Running upward and backward from this process is a well marked line the temporal line which divides into the upper and lower temporal lines continuous and the articulated skull with the corresponding lines on the parietal bone The area below and behind the temporal line is the anterior part of the temporal fossa and gives origin to the temporalis muscle between the super orbital margins the squama projects downward to a level below that of the zygomatic processes This portion is known as the nasal part and presents a rough uneven interval the nasal notch which articulates on either side of the middle line and laterally with the frontal process of the maxilla and with the lacrimal The term nation is applied to the middle of the frontal nasal suture From the center of the notch the nasal process projects downward and forward beneath the nasal bones and frontal processes of the maxilla and supports the bridge of the nose The nasal process ends below and on either side of this is a small groove surface which enters into the formation of the roof of the corresponding nasal cavity The spine forms part of the septum of the nose articulating in front with the crest of the nasal bones and behind with the perpendicular plate of the ethmoid The internal surface of the squama is concave and presents in the upper part of the middle line a vertical groove the sagittal sulcus the edges of which unite below to form a ridge the frontal crest The sulcus lodges the superior sagittal sinus while its margins and the crest afford attachment to the fox cerebri The crest ends below in a small notch which is converted into a foremen the foremen cecum by articulation with the ethmoid This foremen varies in size in different subjects from the pervy and pervious When open it transmits a vein from the nose to the superior sagittal sinus On either side of the middle line the bone presents depressions for the convolutions of the brain and numerous small furrows for the anterior branches of the middle meningeal vessels Several small irregular fossae may also be seen on either side of the sagittal sulcus for the reception of the arachnoid granulations orbital or horizontal part pyrus orbitalis This portion consists of two thin triangular plates the orbital plates which form the vaults of the orbits and are separated from one another by a median gap the ethmoidal notch surfaces the inferior surface on the right is smooth and concave and presents laterally under cover of the zygomatic process a shallow depression the lacrimal fossa for the lacrimal gland near the nasal part is a depression the fovea trochlearis or occasionally a small trochlear spine for the attachment of the cartilaginous pulley of the oblicus oculi superior the superior surface is convex and marked by depressions for the convolutions of the frontal lobes of the brain and faint grooves for the meningeal branches of the ethmoidal vessels the ethmoidal notch separates the two orbital plates it is quadrilateral and filled in the articulated skull by the cremiform plate of the ethmoid the margins of the notch present several half cells which when united with corresponding half cells on the upper surface of the ethmoid complete the ethmoidal air cells two grooves cross these edges transversely they are converted into the anterior and posterior ethmoidal canals by the ethmoid and open on the medial wall of the orbit the anterior canal transmits the nasal ciliary nerve and anterior ethmoidal vessels the posterior ethmoidal nerve and vessels in front of the ethmoidal notch on either side of the frontal spine are the openings of the frontal air sinuses these are two irregular cavities which extend backward, upward and lateralward for a variable distance between the two tables of the skull they are separated from one another by a thin bony septum which often deviates to one or other side with the results that the sinuses are rarely symmetrical absent of birth they are usually fairly well developed between the 7th and 8th years but only reach their full size after puberty they vary in size in different persons and are larger in men than in women footnote Aldrin Turner the accessory of sinuses of the nose 1901 gives the following measurements of the sinus of average size height one and a quarter inches breath one inch depth from before backward one inch and footnote they are lined by mucus membrane and each communicates with the corresponding nasal cavity by means of a passage called the frontal nasal duct borders the border of the squelma is thick strongly serrated level at the expense of the inner table above rest upon the parage of bones and at the expense of the outer table on either side where it receives a lateral pressure of those bones this border is continued below into a triangular rough surface which articulates with the great wing of the sonoid the posterior borders of the orbital plates are thin and serrated and articulate with the small wings of the sonoid structure the squelma and the zygomatic processes are very thick consisting of diploic tissue contained between two compact laminate diploic tissue is absent in the regions occupied by the frontal air sinuses the orbital portion is thin translucent and composed entirely of compact bone hence the facility with which instruments can penetrate the cranium through this part of the orbit when the frontal sinuses are exceptionally large they may extend backward for a considerable distance into the orbital portion which in such cases also consists of only two tables ossification the frontal bone is ossified in membrane from two primary centers one for each half which appear toward the end of the second month of fetal life one above each super orbital margin from each of these centers ossification extends upward to form the corresponding half of the squelma then backward to form the orbital plate the spine is ossified from a pair of secondary centers on either side of the middle line similar centers appear in the nasal part and zygomatic processes at birth the bone consists of two pieces separated by the frontal suture which is usually obliterated except at its lower part by the eighth year but occasionally persists throughout life it is generally maintained that the development of the frontal sinuses begins at the end of the first or beginning of the second year but Onodes researchers indicate that development begins at birth the sinuses are of considerable size for the seventh or eighth year but do not attain the full proportions until after puberty articulations the frontal articulates with balled bones the spinoid the ethmoid the two parietals the two nasals the two maxillae the two lacrimals and the two zygomatics end of section 21 recording by Jennifer Stearns Concord, New Hampshire section 22 of Graze Anatomy part 1 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 1 by Henry Gray the temporal bone part 1 Oz Temporale the temporal bones are situated at the sides and base of the skull each consists of five parts vis the squema the petrus mastoid and tympanic parts and the styloid process the squema squema temporalis the squema forms the anterior and upper part of the bone and is scale like thin and translucent surfaces its outer surface is smooth and convex it affords attachment to the temporalis muscle and forms part of the temporal fossa on its hinder part is a vertical groove for the middle temporal artery a curved line the temporal line or supramastoid crest runs backward and upward across its posterior part it serves for the attachment of the temporal fascia and limits the origin of the temporalis muscle the boundary between the squema and the mastoid portion of the bone as indicated by traces of the original suture lies about one centimeter below this line projecting from the lower part of the squema is a long arched process the zygomatic process this process is at first directed lateral word its two surfaces looking upward and downward it then appears as if twisted inward upon itself and runs forward its surfaces now looking medial word and lateral word the superior border is long thin and sharp and serves for the attachment of the temporal fascia the inferior short thick and arched has attached to it some fibers of the meseter the lateral surface is convex and subcutaneous the medial is concave and affords attachment to the meseter the anterior end is deeply serrated and articulates with the zygomatic bone the posterior end is connected to the squema by two roots the anterior and posterior roots the posterior root a prolongation of the upper border is strongly marked it runs backward across the external acoustic meatus and is continuous with the temporal line the anterior root is continuous with the lower border is short but broad and strong it is directed medial word and ends in a rounded eminence the articular tubercle eminentea articularis this tubercle forms the front boundary of the mandibular fascia and in the fresh state is covered with cartilage in front of the anticular tubercle is a small triangular area which assists in forming the infratemporal fascia this area is separated from the outer surface of the squema by a ridge which is continuous behind with the anterior root of the zygomatic process and in front in the articulated skull with the infratemporal crest on the great wing of the sphenoid between the posterior wall of the external acoustic meatus and the posterior root of the zygomatic process is the area called the supermeatal triangle or mastoid fascia through which an instrument may be pushed into the tympanic atrium at the junction of the anterior root with the zygomatic process is a projection for the attachment of the temporal mandibular ligament and behind the anterior root is an oval depression forming part of the mandibular fascia for the reception of the condyle of the mandible the mandibular fascia glenoid fascia is bound in front by the articular tubercle behind by the tympanic part of the bone which separates it from the external acoustic meatus it is divided into two parts by a narrow slit the petrotympanic fissure gasirian fissure the anterior part formed by the squema is smooth covered in the fresh state with cartilage and articulates with the condyle of the mandible behind this part of the fascia is a small conical eminence this is the representative of a prominent tubercle which in some mammals descends behind the condyle of the mandible and prevents its backward displacement the posterior part of the mandibular fascia formed by the tympanic part of the bone is non-articular this lodges a portion of the pirated gland the petrotympanic fissure leads into the middle ear or tympanic cavity it lodges the anterior process of the milius and transmits the tympanic branch of the anterior maxillary artery the corded tympani nerve passes through a canal canal of jugular separated from the anterior edge of the petrotympanic fissure by a thin scale of bone and situated on the lateral side of the auditory tube in a retiring angle between the squema and the petrus portion of the temporal the internal surface of the squema is concave it presents depressions corresponding to the convolutions of the temporal lobe of the brain and grooves for the branches of the middle meningeal vessels borders the outer is sin and beveled at the expense of the internal table so as to overlap the squamous border of the parietal bone forming with it the squamosal suture posteriorly the superior border forms an angle the parietal notch with the mastoid portion of the bone the entero inferior border is thick serrated and beveled at the expense of the inner table above and of the outer below for articulation with the great wing of the sphenoid mastoid portion pars mastoidia the mastoid portion forms the posterior part of the bone surfaces its outer surface is rough and gives attachment to the occipitalis and auricularis posterior it is perforated by numerous foramina one of these of large size situated near the posterior border is termed the mastoid foramen it transmits the vein to the transverse sinus and a small branch of the occipital artery to the dura mater the position in size of this foramen are very variable it is not always present sometimes it is situated in the occipital bone or in the suture between the temporal and the occipital the mastoid portion is continued below into a conical projection the mastoid process the size and form of which vary somewhat it is larger in the male than in the female this process serves for the attachment of the sternocleidomastoidius splenius capitis and the logisimus capitis on the medial side of the process is a deep groove the mastoid notch digastric fossa at the end of the digastricus medial to this is a shallow furrow the occipital groove which lodges the occipital artery the inner surface of the mastoid portion presents a deep curved groove the sigmoid sulcus which lodges part of the transverse sinus in it may be seen the opening of the mastoid foramen the groove for the transverse sinus is separated from the innermost of the mastoid air cells by a very thin lamina of bone and even this may be partially deficient borders the superior border of the mastoid portion is broad and serrated for articulation with the mastoid angle of the paraietal the posterior border also serrated articulates with the inferior border of the occipital between the lateral angle and the jugular process the mastoid portion is fused with the descending process of the squema above below it enters into the formation of the external acoustic meatus and the tympanic cavity a section of the mastoid process shows it to be hollowed out into a number of spaces the mastoid cells which exhibit the greatest possible variety as to their size and number at the upper and front part of the process are large and irregular and contain air but toward the lower part they diminish in size while those at the apex of the process are frequently quite small and contain marrow occasionally they are entirely absent and the mastoid is then solid throughout in addition to these a large irregular cavity is situated at the upper and front part of the bone it is called the tympanic antrim in the mastoid cells though it communicates with them like the mastoid cells it is filled with air and lined by a prolongation of the mucous membrane of the tympanic cavity with which it communicates the tympanic antrim is bound above by a thin plate of bone the tegman tympani which separates it from the middle fossa of the base of the skull below by the mastoid process and laterally by the squema just below the temporal line and medially by the lateral semicircular canal of the inner ear which projects into its cavity it opens in front into that portion of the tympanic cavity which is known as the attic or epitmpanic recess the tympanic antrim is a cavity of some considerable size at the time of birth the mastoid air cells may be regarded as diverticula and begin to appear at or before birth by the fifth year they are well marked but their development is not completed until toward puberty end of section 22 recorded by David Lawrence in Brampton, Ontario September 2008 section 23 of Grey's Anatomy Part 1 this is a Librevox recording all Librevox recordings are in the public domain for more information or to volunteer please visit Librevox.org recording by Morgan Scorpion Anatomy of the Human Body Part 1 by Henry Grey the temporal bone Part 2 Petrus Portion Pars Petrosa Pyramid the Petrus Portion or pyramid is pyramidal and is wedged in at the base of the skull of the anodinoid and occipital directed medial wood forward and a little upward it presents for examination a base and apex three surfaces and three angles and contains in its interior the essential parts of the organ of hearing base the base is fused with the internal surfaces of the squamous and mastoid portion apex the apex, rough and uneven the angular interval between the posterior border of the great wing of the sphenoid and the basilar part of the occipital it presents the anterior or internal orifice of the carotid canal and forms the postural lateral boundary of the forearm lacquerum surfaces the anterior surface forms the posterior part of the middle fossa of the base of the skull and is continuous with the inner surface of the squamous portion to which it is united by the petrus squamous suture remains of which are distinct even at the late period of life it is marked by depressions for the convolutions of the brain and presents six points for examination one, near the centre and eminence eminentia arcurata which indicates the situation of the superior semicircular canal two, in front of and a little lateral to this eminence a depression indicating the position of the tympanic cavity of bone which separates the tympanic from the cranial cavity is extremely thin and is known as the tegman tympani three a shallow groove sometimes double leading lateralwards and backwards to an oblique opening the hiatus of the facial canal for the passage of the greatest superficial patrosal nerve and the patrosal branch of the middle meningeal artery four, lateral to the hiatus a smaller opening for the passage of the lesser superficial patrosal nerve five, near the apex of the bone the termination of the carotid canal the wall of which in this situation is deficient in front six, above this canal the shallow trigeminal impression for the reception of the semilunar ganglion the posterior surface figure 138 forms the front portion of the posterior fossa of the base of the skull which is continuous with the inner surface of the mastoid portion near the centre is a large orifice the internal acoustic meatus the size of which varies considerably its margins are smooth and rounded and it leads into a short canal about one centimetre in length which runs lateralward it transmits the facial and acoustic nerves and the internal auditory branch of the basilar artery the lateral end of the canal is closed by a vertical plate divided by a horizontal crest the crystal falciformis into two unequal portions figure 140 each portion is further subdivided by a vertical ridge into an anterior and a posterior part in the portion beneath the crystal falciformis are three sets of foramina one group just below the posterior part of the crest situated in the area Cribroso media consists of several small openings for the nerves to the saccule below and behind this area is the foramin singulari or opening for the nerve to the posterior semicircular duct in front of and below the first is a tractus spiralis foraminosis consisting of a number of small spirally arranged openings which encircle the canalis centralis cochliae these openings together with the central canal transmit the nerves to the cochliae the portion above the crystal falciformis presents behind the area Cribrosa superior pierced by a series of small openings for the passage of the nerves to the utricle and the superior and lateral semicircular ducts and in front the area faccians with one large opening the commencement of the canal for the facial nerve aqueductus fallope behind the internal acoustic meatus is a small slit almost hidden by a thin plate of bone leading to a canal the aqueductus vestibuli which transmits the ductus endolymphaticus together with a small artery and vein above and between these two openings is an irregular depression which lodges a process of the duomata and transmits a small vein in the infant this depression is represented by a large fossa the subarculate fossa which extends backwards as a blind tunnel under the superior semicircular canal the inferior surface figure 141 is rough and irregular and forms part of the exterior of the base of the skull it presents 11 points for examination 1. near the apex is a rough surface quadrilateral in form which serves partly for the attachment of the levator velly palatini and the cartilaginous portion of the auditory tube and partly for connection with the basilar part of the occipital bone through the intervention of some dense fibrous tissue 2. behind this is the large circular aperture of the carotid canal which descends at first vertically and then making a bend runs horizontally forward and medial it transmits into the cranium the internal carotid artery and the carotid plexus of nerves 3. medial to the opening for the carotid canal and close to its posterior border in front of the jugular fossa is a triangular depression at the apex of this is a small opening the aqueductus cochliii is a tubular prolongation of the duomata establishing a communication between the paralymphatic space and the subarachnoid space and transmits a vein from the cochlea to join the internal jugular 4. behind these openings is a deep depression the jugular fossa of variable depth and size in different skulls it lodges the bulb of the internal jugular vein 5. in the bony ridge dividing the carotid canal from the jugular fossa is an inferior tympanic canaliculus for the passage of the tympanic branch of the glossopharyngeal nerve 6. in the lateral part of the jugular fossa is the mastoid canaliculus for the entrance of the auricular branch of the vagus nerve 7. behind the jugular fossa is a quadrilateral area the jugular surface covered with cartilage in the fresh state and articulated with the jugular process of the occipital bone extending backward from the carotid canal is the vaginal process a sheath-like plate of bone which divides behind into two laminae the lateral lamina is continuous with the tympanic part of the bone the medial with the lateral margin of the jugular surface 9. between these laminae is the styloid process a sharp spine about 2.5 cm in length 10. between the styloid and mastoid processes is the topanomastoid foramen it is the termination of the facial canal and transmits the facial nerve and stylo-mastoid artery 11. situated between the tympanic portion and the mastoid process is the topanomastoid fissure for the exit of the auricular branch of the vagus nerve 12. angles the superior angle, the longest is grooved for the superior petrosal sinus and gives attachment to the tentorium cerebelli at its medial extremity is a notch in which the trigeminal nerve lies the posterior angle is intermediate in length between the superior and the anterior its medial half is marked by a sulcus which forms with the corresponding sulcus on the occipital bone the channel for the inferior petrosal sinus its lateral half presents an excavation the jugular fossa which with the jugular notch on the occipital forms the jugular foramen an eminence occasionally projects from the centre of the fossa and divides the foramen into two the anterior angle is divided into two parts a lateral joined to the squamous by a suture petrosquamous the remains of which are more or less distinct a medial free which articulates with the spinous process of the sphenoid at the angle of junction of the petrospart on the squamous are two canals one above the other separated by a thin plate of bone the septum canalis muscular tubae processes cochlea reformis both canals lead into the tympanic cavity the upper one semi canalis emtensoris tympani transmits the tensor tympani the lower one semi canalis tubae audita tivae forms the bony part of the auditory tube the tympanic cavity auditory ossicles and internal ear are described with the organ of hearing tympanic part pars tympanica the tympanic part is a curved plate of bone lying below the squamous and in front of the mastoid process surfaces its postural superior surface is concave and forms the anterior wall the floor and part of the posterior wall of the bony external acoustic miatus medially it presents a narrow furrow the tympanic sulcus the attachment of the tympanic membrane its antero inferior surface is quadrilateral and slightly concave it constitutes the posterior boundary of the mandibular fossa and is in contact with the retromandibular part of the parotid gland borders its lateral border is free and rough and gives attachment to the cartilaginous part of the external acoustic miatus internally the tympanic part is fused with the petros portion which is in the retreating angle between it and the squamous where it lies below and lateral to the orifice of the auditory tube posteriorly it blends with the squamous and mastoid part and forms the anterior boundary of the tympanic mastoid fissure its upper border fuses laterally with the back of the post glenoid process while medially it bonds with the petrotympanic fissure the medial part of the lower border is thin and sharp its lateral part splits to enclose the root of the styloid process which is therefore named the vaginal process the central portion of the tympanic part is thin and in a considerable percentage of skulls is perforated by a hole the foramen of hushka the external acoustic miatus is nearly two centimetres long and is directed inward and slightly forward at the same time it forms a slight curve so that the floor of the canal is convex upward in sagittal section it presents an oval or elliptical shape with the long axis directed downward and slightly backward its anterior wall and floor and the lower part of its posterior wall are formed by the tympanic part the roof and upper part of the posterior wall by the squamous its inner end is closed in the recent state by the tympanic membrane the upper limit of its outer orifice is formed by the posterior root of the zygomatic process immediately below which there is sometimes seen a small spine situated at the upper and posterior part of the orifice styloid process processes stylodeus the styloid process is slender pointed and of varying length it projects downwards and forwards from the under surface of the temporal bone its proximal part tympano-hyal is ensheved by the vaginal process of the tympanic portion while its distal part stylohyal gives attachment to the stylohyoid and stylomandibular ligaments and to the styloglossus stylohyodeus and stylofarangius muscles the stylohyoid ligament extends from the apex of the process to the letter corner of the hyoid bone and in some instances is partially in others completely ossified structure the structure of the squamous is like that of the other cranial bones the mastoid portion is spongy and the petros portion is dense and hard ossification the temporal bone is ossified from eight centres exclusive of those for the internal ear and the tympanic ossicles vis one for the squamous including the zygomatic process one for the tympanic part four for the petros and mastoid parts and two for the styloid process just before the close of fetal life figure 142 the temporal bone consists of three principal parts one the squamous is ossified in membrane from a single nucleus which appears near the root of the zygomatic process about the second month two, the petro mastoid part is developed from four centres which make their appearance in a cartilaginous ear capsule about the fifth or sixth month one, prootic appears in the neighbourhood of the eminentia arcurata spreads in front and above the internal acoustic miatus and extends to the apex of the bone it forms part of the cochlea vestibule superior semi-circular canal and medial wall of the tympanic cavity a second opistotic appears at the promontory of the medial wall of the tympanic cavity and surrounds the finestra cochleae it forms the floor of the tympanic cavity and vestibule surrounds the carotid canal invests the lateral and lower part of the cochlea and spreads medially below the internal acoustic miatus a third pterotic, roofs in the carotid and anterum while the fourth, epiotic appears near the posterior semi-circular canal and extends to form the mastoid process feralic three the tympanic ring is an incomplete circle in the concavity of which is a groove the tympanic sulcus for the attachment of the circumference of the tympanic membrane this ring expands to form the tympanic part and is ossified in membrane from a single centre which appears about the third month the styloid process is developed from the proximal part of the cartilage of the 2nd Frankial-Ohioid arch by two centres one for the proximal part, the tympan-Ohio appears before birth the other, comprising the rest of the process is named the stylo-Ohio and does not appear until after birth the tympanic ring unites with the squamous shortly before birth the pteromastoid part and squamous joined during the first year and the tympan-Ohio portion of the styloid process about the same time figures 143 and 144 the stylo-Ohio does not unite with the rest of the bone until after puberty and in some skulls never at all the chief subsequent changes in the temporal bone apart from increase in size r 1, the tympanic ring extends outwards and backwards to form the tympanic part this extension does not however take place at an equal rate all round the circumference of the ring but occurs most rapidly on its anterior and posterior portions and these outgrowths meet and blend and thus for a time there exists in the floor of the meiatus a foramen the foramen of hushka this foramen is usually closed about the fifth year but may persist throughout life 2, the mandibular fossa is at first extremely shallow and looks lateralward as well as downward it becomes deeper and ultimately directed downward the second direction is accounted for as follows the part of the squema which forms the fossa lies at first below the level of the zygomatic process as however the base of the skull increases in width this lower part of the squema is directed horizontally inward to contribute to the middle fossa of the skull and its surfaces therefore come to look upward and downward the attached portion of the zygomatic process also becomes averted and projects like a shelf at right angles to the squema the mastoid portion is at first quite flat and the stylo mastoid foramen and rudimentary stylo process lie immediately behind the tympanic ring with the development of the air cells the outer part of the mastoid portion grows downward and forward to form the mastoid process and the styloid process and stylo mastoid foramen now come to lie on the under surface the descent of the foramen is necessarily accompanied by a corresponding lengthening of the facial canal 4. the downward and forward growth of the mastoid process also pushes forward the tympanic part so that the portion of it which form the original floor of the myatus and contain the foramen of hushka is ultimately found in the interior wall 5. the fossa subarculata becomes filled up and almost obliterated articulations the temporal articulates with five bones occipital, parietal, sphenoid mandible and zygomatic end of section 23 section 24 of grey's anatomy part 1 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 Laurie Ann Walden anatomy of the human body part 1 by Henry Gray the sphenoid bone os sphenoid alley the sphenoid bone is situated at the base of the skull and front of the temporals and basilar part of the occipital it somewhat resembles a bat with its wings extended and is divided into a median portion or body, two great and two small wings extending outward from the size of the body and two pteragoid processes which project from it below body corpus sphenoid alley the body more or less cubicle in shape is hollowed out in its interior to form two large cavities the sphenoidal air sinuses which are separated from each other by a septum surfaces the superior surface of the body presents in front a prominent spine the ethmoidal spine for articulation with the cribreform plate of the ethmoid behind this is a smooth surface slightly raised in the middle line and grooved on either side for the olfactory lobes of the brain this surface is bounded behind which forms the anterior border of a narrow transverse groove the chiasmatic groove or optic groove above and behind which lies the optic chiasma the groove ends on either side in the optic foramen which transmits the optic nerve and ophthalmic artery into the orbital cavity behind the chiasmatic groove is an elevation the tuberculum cellae and still more posteriorly a deep depression the cella tersica the deepest part of which lodges the hypothesis cerebri and is known as the fossa hypothesis the anterior boundary of the cella tersica is completed by two small immanences one on either side called the middle clenoid processes while the posterior boundary is formed by a square shaped plate of bone the dorsum cellae ending at its superior angles and two tubercles the posterior clenoid processes the size and form of which vary considerably in different individuals the posterior clenoid processes deepen the cella tersica and give attachment to the tentorium cerebellae on either side of the dorsum cellae is a notch for the passage of the abducent nerve and below the notch a sharp process the petrosal process which articulates with the apex of the petros portion of the temporal bone and forms the medial boundary of the foramen lacerum the dorsum cellae is a shallow depression the clevis which slopes obliquely backward and is continuous with the groove on the basilar portion of the occipital bone it supports the upper part of the pons the lateral surfaces of the body are united with the great wings and the medial pteragoid plates above the attachment of each great wing is a broad groove curved something like the italic letter f it lodges the internal carotid artery and the cavernous sinus and is named to the carotid groove along the posterior part of the lateral margin of this groove and the angle between the body and great wing is a ridge of bone called the lingula the posterior surface quadrilateral in form is joined during infancy and adolescence to the basilar part of the occipital bone by a plate of cartilage between the 18th and 25th years this becomes ossified ossification commencing above and extending downward the anterior surface of the body presents in the middle line a vertical crest the sphenoidal crest which articulates with the perpendicular plate of the ethmoid and forms part of the septum of the nose on either side of the crest is an irregular opening leading into the corresponding sphenoidal air sinus these sinuses are two large irregular cavities hollowed out of the interior of the body of the bone and separated from one another by a bony septum which is commonly bent to one or the other side they vary considerably in form and size are seldom symmetrical and are often partially subdivided by irregular bony laminate footnote Aldrin Turner gives the following as their average measurements vertical height 7 eighths inch anterior depth 7 eighths inch transverse breadth 3 quarter inch end footnote occasionally they extend into the basilar part of the occipital nearly as far as the foramen magnum they begin to be developed before birth and are of a considerable size by the age of 6 they are partially closed in front and below by two thin curved plates of bone the sphenoidal conchi leaving in the articulated skull a round opening at the upper part of each sinus by which it communicates with the upper and back part of the nasal cavity and occasionally with the posterior ethmoidal air cells the lateral margin of the anterior surface is serrated and articulates with the lamina paparacea of the ethmoid completing the posterior ethmoidal cells the lower margin articulates with the orbital process of the palatine bone and the upper with the orbital plate of the frontal bone the inferior surface presents in the middle line a triangular spine the sphenoidal rostrum which is continuous with the sphenoidal crest on the anterior surface and is received in a deep fissure between the ally of the vomer on either side of the rostrum is a projecting lamina the vaginal process directed medial word from the base of the medial pteragoid plate with which it will be described the great wings alley magni the great wings or alasphenoids are two strong processes of bone which arise from the sides of the body and are curved upward lateral word and backward the posterior part of each projects is a triangular process which fits into the angle between the squema and the petrus portion of the temporal and presents at its apex a downwardly directed process the spina angularis or sphenoidal spine surfaces the superior or cerebral surface of each great wing forms part of the middle fossa of the skull it is deeply concave and presents depressions for the convolutions of the temporal lobe of the brain at its anterior and medial part is a circular aperture the foramen rotundum for the transmission of the maxillary nerve behind and lateral to this is the foramen ovale for the transmission of the mandibular nerve it is an accessory minangeal artery and sometimes the lesser superficial patrosal nerve footnote the lesser superficial patrosal nerve sometimes passes through a special canal canaliculus inominatus of Arnold situated medial to the foramen spinosum end footnote medial to the foramen ovale a small aperture the foramen vasalee may occasionally be seen opposite the root of the process it opens below near the scaphoid fossa and transmits a small vein from the cavernous sinus lastly in the posterior angle near to and in front of the spine is a short canal sometimes double the foramen spinosum which transmits the medial minangeal vessels and a recurrent branch from the mandibular nerve the lateral surface is convex and divided by a transverse ridge into two portions the superior or temporal portion convex from above downward concave from before backward forms a part of the temporal fossa and gives attachment to the temporalis the inferior or infratemporal smaller in size and concave enters into the formation of the infratemporal fossa and together with the infratemporal crest affords attachment to the teregoidus externus it is pierced by the foramen ovale and foramen spinosum and at its posterior part is the spina angularis which is frequently grooved on its medial surface for the corda tempani nerve two the spina angularis are attached the sphenomandibular ligament and the tensorvelli palatini medial to the anterior extremity of the infratemporal crest is a triangular process which serves to increase the attachment of the teregoidus externus extending downward and medialward from this process onto the front part of the lateral teregoid plate is a ridge which forms the anterior limit of the infratemporal surface and in the articulated skull the posterior boundary of the terego maxillary fissure the orbital surface of the great wing smooth and quadrilateral in shape is directed forward and medialward and forms the posterior part of the lateral wall of the orbit its upper serrated edge articulates with the orbital plate of the frontal its inferior rounded border forms the postural lateral boundary of the inferior orbital fissure its medial sharp margin forms the lower boundary of the superior orbital fissure and has projecting from about its center a little tubercle of the rectus lateralis oculi at the upper part of this margin is a notch for the transmission of a recurrent branch of the lacrimal artery its lateral margin is serrated and articulates with the zygomatic bone below the medial end of the superior orbital fissure is a grooved surface which forms the posterior wall of the terego palatine fossa and is pierced by the foramen rotundum margin convincing from behind that portion of the circumference of the great wing which extends from the body to the spine is irregular its medial half forms the anterior boundary of the foramen lacerum and presents the posterior aperture of the teregoid canal for the passage of the corresponding nerve and artery its lateral half articulates by means of a synchondrosis with the petrus portion of the temporal and between the two bones of the skull is a furrow the sulcus tubae for the lodgement of the cartilaginous part of the auditory tube in front of the spine the circumference presents a concave serrated edge beveled at the expense of the inner table below and of the outer table above for articulation with the temporal squema at the tip of the great wing is a triangular portion beveled at the expense of the internal surface for articulation with the sphenoidal angle of the parietal bone this region is named the tereon medial to this is a triangular serrated surface for articulation with the frontal bone this surface is continuous medially with the sharp edge which forms the lower boundary of the superior orbital fissure and laterally with the serrated margin for articulation with the zygomatic bone the small wings the small wings or orbitos phenoids are two thin triangular plates which arise from the upper and anterior parts of the body and projecting lateral word and in sharp points surfaces the superior surface of each is flat and supports part of the frontal lobe of the brain the inferior surface forms the back part of the roof of the orbit and the upper boundary of the superior orbital fissure this fissure is of a triangular form and leads from the cavity of the cranium into that of the orbit it is bounded medially by the body above by the small wing below by the medial margin of the orbital surface of the great wing and is completed laterally by the frontal bone it transmits the oculomotor trochlear and abducent nerves the three branches of the ophthalmic division of the trigeminal nerve some filaments from the cavernous plexus of the sympathetic the orbital branch of the middle meningeal artery a recurrent branch from the lacrimal artery to the dural motor and the ophthalmic vein borders the anterior border is serrated for articulation with the frontal bone the posterior border smooth and rounded is received into the lateral fissure of the brain the anterior clenoid process which gives attachment to the tentorium cerebelli it is sometimes joined to the middle clenoid process by a spicule of bone and when this occurs the termination of the groove for the internal carotid artery is converted into a foramen carotico-clenoid the small wing is connected to the body by two roots the upper, thin and flat the lower, thick and triangular between the two roots is the optic foramen for the transmission of the optic nerve and ophthalmic artery pteragoid processes processes pteragoidiii the pteragoid processes one on either side descend perpendicularly from the regions where the body and great wings unite each process consists of a medial and a lateral plate the upper parts of which are fused anteriorly a vertical sulcus the pterago palatine groove descends on the front of the line of fusion the plates are separated below by an angular cleft the pteragoid fissure the margins of which are rough for articulation with the pyramidal process of the palatine bone the two plates diverge behind and enclose between them a V-shaped fossa the pteragoid fossa which contains the pteragoidius internus and tensor phthalatini above this fossa is a small oval shallow depression the scaphoid fossa which gives origin to the tensor phthalatini the anterior surface of the pteragoid process is broad and triangular near its root where it forms the posterior wall of the pterago palatine fossa and presents the anterior orifice of the pteragoid canal lateral pteragoid plate the lateral pteragoid plate is broad thin and averted its lateral surface forms part of the medial wall of the infratemporal fossa and gives attachment to the pteragoidius externus its medial surface forms part of the pteragoid fossa and gives attachment to the pteragoidius internus medial pteragoid plate the medial pteragoid plate is narrower and longer than the lateral it curves lateral word at its lower extremity into a hook-like process the pteragoid hamulus around which the tendon the tensor valley palatini glides the lateral surface of this plate forms part of the pteragoid fossa the medial surface constitutes the lateral boundary of the coena or posterior aperture of the corresponding nasal cavity superiorly the medial plate is prolonged onto the under surface of the body as a thin lamina named the vaginal process which articulates in front with a sphenoidal process of the palatine and behind this is the ala of the vomer the angular prominence between the posterior margin of the vaginal process and the medial border of the scaphoid fossa is named the pteragoid tubercle and immediately above this is the posterior opening of the pteragoid canal on the under surface of the vaginal process is a furrow which is converted into a canal by the sphenoidal process of the palatine bone for the transmission of the pharyngeal branch of the vaginal maxillary artery and the pharyngeal nerve from the sphenopalatine ganglion the pharyngeal aponeurosis is attached to the entire length of the posterior edge of the medial plate and the constrictor takes origin from its lower third projecting backward from near the middle of the posterior edge of this plate is an angular process the processes tuberous which supports the pharyngeal end of the auditory tube the anterior margin of the plate articulates with the posterior border of the vertical part of the palatine bone the sphenoidal conchi conchi sphenoidalis sphenoidal terminated processes the sphenoidal conchi are two thin curved plates situated at the anterior and lower part of the body of the sphenoid an aperture of variable size exists in the anterior wall of each and through this the sphenoidal sinus opens into the nasal cavity each is irregular in form and tapers to a point behind being broader and thinner in front its upper surface is concave and looks toward the cavity of the sinus its under surface is convex and forms part of the roof of the corresponding nasal cavity each bone articulates in front with the ethmoid laterally with the palatine its pointed posterior extremity of the vomer and is received between the root of the pteragoid process laterally and the rostrum of the sphenoid medially a small portion of the sphenoidal concha sometimes enters into the formation of the medial wall of the orbit between the lamina paparacea of the ethmoid in front the orbital plate of the palatine below and the frontal bone above ossification until the seventh or eighth month of fetal life the body of the sphenoid consists of two parts that is, one in front of the tuberculum cellae the pre-sphenoid with which the small wings are continuous the other comprising the cellatursica and dorsum cellae the post-sphenoid with which are associated the great wings and pteragoid processes the greater part of the bone is ossified in cartilage there are fourteen centers in all six for the pre-sphenoid and eight for the post-sphenoid pre-sphenoid about the ninth week of fetal life an ossific center appears for each of the small wings orbitosphenoids just lateral to the optic foramen shortly afterward two nuclei appear in the pre-sphenoid part of the body the sphenoidal concha are each developed from a center which makes its appearance about the fifth month at birth they consist of small triangular laminae and it is not until the third year that they are all ad out and cone shaped about the fourth year they fuse with the labyrinths of the ethmoid and between the ninth and twelfth years they unite with the sphenoid footnote according to cleland each sphenoidal concha is ossified from four centers end footnote post-sphenoid the first ossific nuclei are those for the great wings alasphenoids footnote the example of anatomy 1906 states that the pteragoid center appears first in an embryo 57 days old end footnote one makes its appearance in each wing between the foramen retundum and foramen avali about the eighth week the orbital plate and that part of the sphenoid which is found in the temporal fossa as well as the lateral pteragoid plate are ossified in membrane faucet soon after the centers for the post-sphenoid part of the body appear one on either side of the salatursica and become blended together about the middle of fetal life each medial pteragoid plate with the exception of its hamulus is ossified in membrane and its center probably appears about the ninth or tenth week the hamulus becomes conchified during the third month and almost at once undergoes ossification faucet the medial joins the lateral pteragoid plate about the sixth month about the fourth month a center appears for each lingula and speedily joins the rest of the bone the pre-sphenoid is united to the post-sphenoid about the eighth month and at birth the bone is in three pieces a central consisting of the body and small wings and two lateral each comprising a great wing and pteragoid process in the first year after birth the great wings and body unite and the small wings extend inward above the anterior part of the body and meeting with each other in the middle line form an elevated smooth surface termed the jugum sphenoid alley by the 25th year the sphenoid and occipital are completely fused between the pre and post-sphenoid there are occasionally seen the remains of a canal the canalis craniofaryngeus through which in early fetal life the hypothaseal diverticulum of the buccal ectoderm is transmitted the sphenoidal sinuses are present as minute cavities at the time of birth but do not attain their full size until after puberty intrinsic ligaments of the sphenoid the more important of these are the pterago spinus stretching between the spinaangularis and the lateral pteragoid plate C. cervical fascia the interclinoid a fibrous process joining the anterior to the posterior clinoid process and the carotico-clinoid connecting the anterior to the middle clinoid process these ligaments occasionally ossify articulations the sphenoid articulates with 12 bones 4 single the vomer, ethmoid, frontal and occipital and 4 paired the parietal, temporal, zygomatic and palatine footnote it also sometimes articulates with the tuberosity of the maxilla end footnote end of section 24 section 25 of Grey's Anatomy Part 1 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 Lorraine Walden Anatomy of the Human Body Part 1 by Henry Gray section 25 ethmoid bone os ethmoid alley the ethmoid bone is exceedingly light and spongy and cubical in shape it is situated at the anterior part of the base of the cranium between the two orbits at the roof of the nose and contributes to each of these cavities it consists of four parts a horizontal or a cribreform plate forming part of the base of the cranium a perpendicular plate constituting part of the nasal septum and two lateral masses or labyrinths cribreform plate lamina cribrosa horizontal lamina the cribreform plate is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities projecting upward from the middle line of this plate is a thick smooth triangular process the crista galley so called from its resemblance to a cox comb the long thin posterior border of the crista galley serves for the attachment of the fox cerebrae its anterior border, short and thick articulates with the frontal bone and presents two small projecting ally which are received into corresponding depressions in the frontal bone and complete the foramen cecum its sides are smooth and sometimes bulging from the presence of a small air sinus in the interior on either side of the crista galley the cribreform plate is narrow and deeply grooved it supports the olfactory bulb and is perforated by foramina for the passage of the olfactory nerves the foramina in the middle of the groove are small and transmit the nerves to the roof of the nasal cavity those at the medial and lateral parts of the groove are larger the former transmit the nerves to the upper part of the nasal septum the latter those to the superior nasal conca at the front part of the cribreform plate on either side of the crista galley is a small fissure which is occupied by a process of neuromatter lateral to this fissure is a notch or foramen which transmits the nasal ciliary nerve from this notch a groove extends backward to the anterior ethmoidal foramen perpendicular plate lamina perpendicularis vertical plate the perpendicular plate is a thin flattened lamina polygonal inform which descends from the under surface of the cribreform plate and assists in forming the septum of the nose it is generally deflected a little to one or the other side the anterior border articulates with the spine of the frontal bone and the crest of the nasal bones the posterior border articulates by its upper half with a sphenoidal crest by its lower with the vomar the inferior border is thicker than the posterior and serves for the attachment of the septal cartilage of the nose the surfaces of the plate are smooth except above where numerous grooves and canals are seen these lead from the medial foramina on the cribreform plate and lodge filaments of the olfactory nerves the labyrinth or lateral mass labyrinthus ethmoidalis consists of a number of thin walled cellular cavities the ethmoidal cells arranged in three groups anterior, middle, and posterior and interposed between two vertical plates of bone the lateral plate forms part of the orbit the medial part of the corresponding nasal cavity in the disarticulated bone many of these cells are opened into but when the bones are articulated they are closed in at every part except where they open into the nasal cavity surfaces the upper surface of the labyrinth presents a number of half broken cells the walls of which are completed in the articulated skull by the edges of the ethmoidal notch of the frontal bone crossing this surface are two grooves converted into canals by articulation with the frontal they are the anterior and posterior ethmoidal canals and open on the inner wall of the orbit the posterior surface presents large irregular cellular cavities which are closed in by articulation with the sphenoidal conca and orbital process of the palatine the lateral surface is formed of a thin smooth oblong plate the lamina paperasia osplanum which covers in the middle and posterior ethmoidal cells and forms a large part of the medial wall of the orbit it articulates above with the orbital plate of the frontal bone also with the maxilla and orbital process of the palatine in front with the lacrimal and behind with the sphenoid in front of the lamina paperasia are some broken air cells which are overlapped and completed by the lacrimal bone and the frontal process of the maxilla a curved lamina the unsinnet process projects downward and backward from this part of the labyrinth it forms a small part of the medial wall of the maxillary sinus and articulates with the ethmoidal process of the inferior nasal conca the medial surface of the labyrinth forms part of the lateral wall of the corresponding nasal cavity it consists of a thin lamella which descends from the under surface of the cribriform plate and ends below in a free convoluted margin the middle nasal conca it is rough and marked above by numerous grooves directed vertically downward from the cribriform plate they lodge branches of the olfactory nerves which are distributed to the mucous membrane covering the superior nasal conca the back part of the surface is subdivided by a narrow oblique fissure, the superior miatus of the nose bounded above by a thin curved plate, the superior nasal conca the posterior ethmoidal cells open into this miatus below and in front of the superior miatus is the convex surface of the middle nasal conca it extends along the whole length of the medial surface of the labyrinth and its lower margin is free and thick the lateral surface of the middle conca is concave and assists in forming the middle miatus of the nose the middle ethmoidal cells open into the central part of this miatus and a sinuous passage, termed the infundibulum extends upward and forward through the labyrinth and communicates with the anterior ethmoidal cells and in about 50% of skulls is continued upward as the frontal nasal duct into the frontal sinus ossification the ethmoid is ossified in the cartilage of the nasal capsule by three centers, one for the perpendicular plate and one for each labyrinth the labyrinths are first developed, ossific granules making their appearance in the region of the lamina paperasia between the 4th and 5th months of fetal life and extending into the conca at birth the bone consists of the two labyrinths which are small and ill developed during the first year after birth the perpendicular plate and crystal golly begin to ossify from a single center and are joined to the labyrinths about the beginning of the second year the creeper form plate is ossified from the perpendicular plate and partly from the labyrinths the development of the ethmoidal cells begins during fetal life articulations the ethmoid articulates with 15 bones four of the cranium the frontal, the sphenoid and the two sphenoidal conchi and 11 of the face the two nasals, two mexile two lacrimals, two palitines two inferior nasal conchi and the vomer sutural or wormian bones footnote Ole Verm, professor of anatomy at Copenhagen 1624-1639 was erroneously supposed to have given the first detailed description of these bones in footnote in addition to the usual centers of ossification of the cranium others may occur in the course of the sutures giving rise to irregular isolated bones the sphenoidal conchi and the sphenoidal conchi they occur most frequently in the course of the landoidal suture but are occasionally seen at the fontanelles especially the posterior one, the terion ossicle sometimes exists between the sphenoidal angle of the parietal and the great wing of the sphenoid they have a tendency to be more or less symmetrical on the two sides of the skull and very much in size their number is generally limited to two or three but more than a hundred have been found in the skull of an adult hydrocephalic subject