Soine bones are whollygelatinous, others wholly membranous, and others partly in the one and partly in the other state. 91. The process of ossification commences at about the end of the second month, but not in all parts of the skeleton. In some parts the process does not begin till after birth. For the mode in which ossification proceeds, refer to the article PHYSIOLOGY, Marrow does not appear in its proper form till after birth; indeed this fluid does not acquire the consistency of true medullary oil until the period of maturity. In old persons the membrane common to the marrow becomes less vascular, and the oil itself acquires a yellow colour. The periosteum is thicker, more tender, and more vascular in the fœtus than in the adult; in old persons the reverse is the case. As soon as the soft rudiments of the future bones are visible in the fœtus, divisions may be observed in them corresponding to the articulations and synchondrosis, but none to the sutures. The ligaments and synovial membranes in the young person differ only in size from those of the adult. ANATOMY OF PARTICULAR PARTS OF THE 92. Bones and sutures of the cranium. The bones of the cranium are eight; or, according to some, ten in number. The difference of enumeration depending upon whether the petrous portion of the temporal bones are regarded, or not, as distinct bones. The eight bones are, the os frontis; the two parietal bones; the os occipitis; the ossa temporum; the os sphenoides; and os ethmoides. passes through two small holes into the nostrils, which it serves to moisten. 94. The parietal bones are two: in some places they are thin and almost transparent. They are of an irregular square figure, and are bordered with indentations through their whole circumference, except at the lower part. These bones form a kind of vault to the cranium. On their inner surface the marks of the vessels of the dura mater are observed, and at their upper edge is found the groove for the superior longitudinal sinus. 95. The occipital bone forms the back and inferior part of the skull; it has considerable indentations. At its inferior portion is a large foramen, through which the medulla oblongata passes into the spine, or into the brain, as some anatomists would express themselves. This bone is bounded by the temporal, sphenoidal, and parietal bones. In its inside is a conical spine impressed by the longitudinal and lateral sinuses; and on the outside, opposite to the middle of this spine in some bodies, is an apophysis; and from that down to the great foramen a small thin spine: in most skulls a foramen is found behind each apophysis; through these pass sinuses from the lateral sinus to the external cervical veins. 96. The temporal bones are two, or according to some anatomists four, the petrous portions being considered by these last as distinct bones. These bones have several processes and cavities; one anterior called the zygomatic; one posterior called the mastoid, or mamillary, from its resemblance to a nipple; and one inferior named the styloid, because it is shaped like a stiletto or dagger. 97. The cavities of the temporal bones are the meatus auditorius externus; 2. a large fossa, which serves for the articulation of the lower jaw; it is before the meatus, and under the zygomatic process; 3. the styloi-mastoid foramen, so named from its situation between the styloid and mastoid process; it is likewise called the aquedect of Fallopius, Fallopius, and affords a passage for the portio dura of the seventh pair of nerves; 4. below, and on the fore-part of the last foramen, we observe part of the jugular fossa, in which the beginning of the internal jugular vein is lodged. Anterior and superior to this is the orifice of a foramen through which passes the carotid artery; and at this part of the bone the opening of the Eustachian tube is to be seen, a canal passing from the ear into the pharyngal cavity. 93. Os Frontis. - This forms the upper and fore part of the cranium. It is outwardly convex, its concave surface being towards the brain. Its lower parts compose the superior portions of the orbits of the eyes. In the centre of the inferior part of this bone is placed also the ethmoid bone, which is situated at the top of the cavity of the nostrils. On the exterior surface of the frontal bone there are five processes: one placed at the bottom and narrowest part is called the nasal. The four others are called angular or orbitar processes, which assist to form the orbits. In the middle of the bone, above the os ethmoides, most commonly a thin spine, by which this part of the bone is strengthened. This is not always present, but when it is absent the skull is thicker than usual at this part and from its middle externally a process issues which supports the bones of the nose. Immediately above the ethmoid bone, in this bone, is a small 98. The petrous portion of this bone is of a blind hole through which a vein passes into the triangular figure which separates two fossæ; one longitudinal sinus of the dura mater; and, on the superior and anterior, the other inferior and posupper edge of each orbit, a small perforation or terior; the latter of these composes part of the notch is found, through which nerves and an fossa in which the cerebellum is placed; and the artery pass to the forehead. There is also a small former a portion of the last fossa for the bases of foramen in each orbit, through which passes a the brain. On the posterior side of the parspebranch of what are called the fifth pair of nerves. trosa is observed the meatus auditorius externus, This bone is, almost throughout its whole sub- into which enters the double nerve of the seventh stance, composed of two tables, which separating pair. On the under side of this process part of from each other under the eyes form two cavities, a hole appears, which is common to the temone on each side of the bone, called frontal si- poral and occipital bones; through it the lateral nuses. In these sinuses a mucus is secreted sinus, the eighth pair and accessory nerves from their internal membrane, which constantly pass. 99. This hard portion of the temporal bones contains the bones of the ear. The temporal bones are joined to the ossa malarum, to the parietal bones, to the occipital bone, and to the sphenoid bone. 100. The os ethmoides, or sieve-like bone, is about two inches in circumference; it is situated in the anterior part of the basis of the skull. It is pierced by a number of foramina, through which the olfactory nerves pass. From its middle arises a large process named crista galli, and opposite to this a thin one, which in part divides the nose. The greater part of the laminæ spongiosæ in the nose belongs to this one. 101. The os sphenoides is of a very irregular shape; it is seated in the middle of the basis of the skull, and is bounded by the os frontis, ethmoides, vomer, occipitis maxillæ superioris, ossa parietalia, palati, malarum, and temporum. In its inside, next the brain, is a cavity named sella turcica, which is bounded by four processes called clinoid; under the two foremost of which pass the internal carotid arteries, and from their outsides are continued two thin long processes upon that part of the frontal bone which separates the anterior from the posterior lobes of the brain. Opposite to the cella turcica is a process which makes part of the exterior of the nose. On the outside of the skull, adjoining the upper jaw, are two processes of this bone on each side, named pterygoid, from which arises one on each side near the palate, which have no name. Over these pass the tendons of the pterygostaphalini externi muscles; and more towards the occiput, between these and the styloid processes of the temporal bones, arise two small rugged processes. Under the sella turcica a sinus or two is mostly found in adults, but in children consisting only of such a spongy substance as is seen in the ends of some of the bones. At the inside of the basis of the two anterior clinoid processes are two round holes, which are the first foramina of the skull; through these the optic nerves pass. Nearly under these, towards the sides of the skull, are two irregular slits, named foramina lacera, or the second foramina of the skull, through which pass nerves and blood-vessels into the orbits. Under these, towards the occiput, are two round foramina, making the third, and through which pass nerves to the face. About half an inch nearer the occiput are two more of an oval figure, which are the fourth foramina, and through which pass the largest branches of the fifth pair of nerves. Very little further are two very small ones, called the fifth, through which enter branches of the carotid artery to the dura mater. Between the sphenoid and the petrous portion of the temporal Done are found two large irregular foramina, in which large veins are sometimes seen; and from these, through part of the bone under the pterygoid processes, proceed the small apertures through which pass arteries to the back of the nose. 102. The sutures of the cranium are the following: 1. The coronal suture which joins the parietal bones to the frontal; it runs across the skull from one upper edge of the sphenoidal bone to the other. 2. the sagittal suture join ing the parietal bones together; it issues from the central upper part of the frontal bone, and is continued over the head to the occipital bone. In children the frontal bone is divided into two by a continuation of this suture through the os frontis down to the nose; this is sometimes the case in the adult, when the frontal bone is of course divided like the parietal into two. 3. the squamous suture is formed by the upper part of the temporal and sphenoidal bones wrapping over the lower edge of the parietal bones. 5. The transverse suture runs through the bottoms of the orbits, and joins the lower edge of the frontal bone to the os sphenoides, maxıllæ superioris, ossa nasi, unguis, plana, palati, and malarum. BONES OF THE FACE AND MOUTH. 103. The face is divided into the superior and inferior maxilla. The first, that is the upper jaw, is formed of thirteen bones exclusive of the teeth; these are the two superior maxillary, two nasal, two palatine, two malar, two inferior spongy, two lachrymal, and the vomer; these are united to the cranium and to one another by harmony. The inferior maxilla, or under-jaw, is formed of one bone. 104. The superior maxillary bone consists of two parts; is in fact two bones, although sometimes described as a single one. It has two processes, which join the os frontis and constitute part of the nose; and a third which joins to the cartilage of the septum nasi. Its upper and outer parts compose the lower portions of the orbits; its inferior sides all that part of the face and the cheeks, eyes and nose, to the mouth, and two-thirds of the roof of the mouth. A little below the orbits are two holes, and behind the incisores teeth one more, which divides into two as it opens into the nose on each side of the septum nasi. Between the posterior molares and the orbits are two great sinuses, called antra maxillæ superioris, which open into the upper part of the nose. In the lower edge of this jaw are the sockets or alveoli for the teeth. All the body of this bone is hollow, forming a large sinus, which is commonly named antrumhighmorianum. This antrum appears in the separate bone to have a large aperture into the nostrils; but in recent subjects it is so covered at its back part by the palate-bone, in the middle by the inferior sponge-bone, and anterior by a strong membrane, that one, and sometimes two holes, scarcely so large as a crow-quill, are only left at the upper part, which after a short winding process open into the nostrils between the two spongy bones. At the bottom of this cavity we may often observe some protuberances in which the small points of the roots of the teeth are contained. The cavity and the sockets of the teeth are often divided by the interposition of only a very thin bony plate. 105. The ossa malarum form the anterior, inferior, and outer parts of the orbits. They have each a short process, which joins the processus jugales of the temporal bones, and form arches which have been named ossa jugalia. whole of the malar bone is by some indeed called jugal. The 106. The ossa nasi constitute the upper part of the nose, and form that arch which is called the bridge of the nose. 107. The ossa unguis, or lachrymalia, are situated immediately below the frontal bone towards the nose and within the orbits, the anterior and inner parts of which they help to compose. Between each of them and the upper jaw a foramen is found, as large as a goose-quill, for the passage of the lachrymal duct into the nose. 108. The ossa palati are small and of a very irregular figure; they form the back part of the roof of the mouth, and a small part of the bottom of each orbit. Between the palatine and maxillary bones, near the pterygoid process of the sphenoid, are two small foramina, through which arteries and nerves pass to the palate. 109. The spongy bones are situated in the sides and lower part of the nostrils; they are considered by some as merely the spongy laminæ of the ethmoid: and some anatomists further describe two planar bones which are also rather parts of their spongy surfaces than properly separate bones. 110. The vomer, so called from its supposed resemblance to the ancient plough-share, is placed between the bones of the palate and the sphenoidal bone. It divides the nostrils into two parts, forming with its cartilage the septum nasi. 111. The inferior maxillary, or lower jawbone, occupies the whole inferior and anterior part of the face. The shape of the bone is something like that of a horse-shoe. It is articulated with the temporal bones by the condyloid processes. Near these arise two others called coronal; and at the inside of the chin a small rough process called processus inominatus. In the inside of this bone, under each coronal process, is a large foramen which runs under the teeth and passes out near the chin. Through this the vessels pass which belong to the teeth; and in the upper edge of the jaw are the alveoli, or sockets for the teeth. 113. Each tooth is divided into a crown, which is covered by the enamel; a nut, or the part embraced by the gum; and a root, or fang, which last is hidden within the socket. 114. The teeth are of four kinds; viz. incisores, cuspidati, bicuspides, and molares. The first are eight in number, four in each jaw; they are placed in the front of the mouth, are flat, and sharp-edged; the roots, or fangs, are simple: those of the upper jaw are fixed obliquely backwards, so that they generally cover a small part of the incisores of the under jaw. The cuspidati are four in number, one cuspidatus being placed on each side of the incisores. The fang of these teeth is single, and goes a considerable way under the jaw, especially the two of the upper jaw which have been called the eye-teeth, under the supposition that the fangs reached the eye. The end of these teeth is pointed, their bodies being rounded. The bicuspides are eight, as there are two on the side of each cuspidatus; they appear, at both extremities, as if formed by the junction of two incisores. The molares are twelve, three are situated at the extremities of each jaw. The fangs of these are varied; those of the under-jaw have two, and of the upper-jaw three. Their oral extremities are full of irregularities. The two last are called sapientiæ, from the lateness of their appearance. 115. The first set of teeth consists of twenty. For the rationale of dentition, and mode in which the first are displaced to make way for the second set, consult the article PHYSIOLOGY. OS HYOIDES. 116. This is a detached bone, placed at the root of the tongue, and has some resemblance to the Greek letter v, whence its name. This bone is convex, and irregular at its fore part; and unequally concave at its interior surface. Its uses are to support the tongue, and give attachment to a considerable number of muscles; some of which are proper to the tongue, while others belong to the fauces and larynx. At birth this bone is principally cartilaginous. BONES OF THE TRUNK. From 117. The trunk is formed of the spine, the thorax, and the pelvis; the first of which is made up of twenty-four bones called vertebræ; to which are added the sacral bone, and os coccygis. The vertebræ are divided into cervical, which are seven; into dorsal, which are twelve; and into lumbar, which are five in number. The first vertebra of the neck is called atlas. The bodies of these vertebræ are smaller, and of a firmer texture than the other vertebræ. the middle of the posterior part of each vertebra, except the first, stands a process which is named spinal; and from every one there is a process on each side called transverse; while there are two upper and two under ones that are shorter, which are named the superior and inferior oblique processes. The fore part of the seven vertebræ of the neck, and two upper ones of the back, are anteriorly flat. The third and fourth of the back are acute. The spinal processes of the second, third, fourth, and fifth, of the cervical vertebræ are forked; the two last long and horizontal, as are the three or four upper ones of the back: these last, however, are a little declining. The middle ones of the dorsal run obliquely downwards, and the processes of the remaining vertebræ become successively thicker, stronger, and less declining, those of the loins being horizontal. The transverse processes of the cervical vertebræ are perforated for the admission of the cervical blood-vessels. The eight or nine superior ones of the back receive the upper ribs; and the rest, with those of the loins, serve only for the origin and insertion of muscles. 118. The os sacrum has two upper oblique processes, some small spinal processes, and two foramina in each interstice of the bones which compose it, both before and behind. 119. The os coccygis is formed of a chain of bones, each piece becoming smaller as it descends; it is convex behind, and concave anteriorly; it is triangular in its form. At birth it is cartilaginous; and in old age the separate pieces of which it is made up become firmly united; and with the os sacrum become one continued mass of bone. 120. Through every bone of the spine, the os coccygis excepted, there is a large foramen, which, together, make up the long channel for the passage of the medulla-spinalis, and in each space between the vertebræ are two large foramina for the passage of the several nerves. 121. The bodies of the vertebræ are all connected by strong ligaments or intervening cartilages. In the cervical portion of the bohy column, the oblique processes are wrapped over those of the receiving bone. It is the same with the dorsal vertebræ. The vertebræ of the loins are received into deep cavities, and are attached by strong ligaments. 122. The ribs are twelve in number on each side; the seven uppermost being generally called true ribs, their cartilages reaching the sternum; and the five lowest are called false. They are articulated to the twelve vertebræ of the back, and all, except the two or three last ones, are articulated to the transverse processes of the vertebræ. The substance of the ribs is cellular and spongy, with a thin lamellated surface, which, as it approaches the vertebræ, becomes thicker and stronger. To the fore end of each rib, a long, broad, and strong cartilage is fixed, and thence reaches to the sternum, or is joined to the cartilage of the next rib. These cartilages make a considerable curve, their concave part being upwards; in old persons they often become very much ossified. 123. The sternum, or breast-bone, is mostly composed of three spongy bones, sometimes of more. To this two of the cartilages of the ribs are attached. At the inferior extremity of the sternal bone, what is called the ensiform cartilage is attached. This is situated at the part which is called the pit of the stomach. The number of the vertebræ, and also of the ribs, is subject to slight variations. 124. The pelvis. This is so named from its resemblance to a basin formerly used by barbers. It constitutes in a manner the base of the skeleton's trunk. Four bones enter into its composition: viz. two ossa inominata, the os sacrum, and the os coccygis. The ossa inominata are composed of three bones, which in young persons are separate: viz. the ilium, and the ischium, and the os pubis; the first being placed uppermost, the second the lowest, and the third anteriorly. In the centre of these bones is the acetabulum, or socket for receiving the round extremity, or head, as it is called, of the thighbone. 125. There is a considerable difference in the form and cavity of the male and female pelvis. In the latter the sacral bone is shorter and broader, and the iliac portions of the ossa inominata are more expanded; so that the brim of the pelvis, in females, is nearly of an oval shape, being considerably wider from side to side, than from the junction of the two ossa pubis to the sacrum; the ischia, too, are more separated from each other in the female pelvis, so that the lower part of the pelvis is likewise wider than in man, and the sacrum though shorter is more hollowed; while the os coccygis is more moveable, from being more loosely connected with the sacrum. BONES OF THE LOWER EXTREMITIES. 126. Each lower extremity is divided into three parts, the thigh, the leg, and the foot; to which the patella or knee-bone may be added. 127. Os femoris, or femur, is the single bone by which the thigh is formed. It is a long cylindrical bone, situated between the pelvis and the leg; its head, which as we have just said is received into the acetabulum, has a small depression in the middle for the attachment of the round or restraining ligament. The neck, which is between the body of the bone and its head, is rough and gives attachment to the capsular ligament. What is called the great trochanter of the femur is a large unequal eminence below its neck; and then there is another named the small trochanter. The body of the os femoris is smooth and convex before and hollow posteriorly, where there is a rough line called linea aspera. 128. The leg consists of three bones; the tibia, the fibula, and the patella. 129. The tibia is a long, thick, triangular and cylindrical bone placed between the femur and tarsus in the anterior and inside of the leg. It is thickest at its upper extremity. Its anterior ridge or angle is called the spine or shin; at the lower end of this bone a considerable process is found which forms the inner ancle. 130. The fibula is a longitudinal bone situated at the outer part of the leg by the side of the tibia. The process which is at the lower extremity of this bone forms the outer ancle. It is connected to the tibia by an interosseous ligament. 131. The patella rotula, or knee-pan, is a small triangular spongy bone, situated between the interior extremity of the thigh bone and upper part of the tibia. It is connected to the condyles of the femur and also to the tibia. 132. The foot bones are distinguished into three orders: viz. the tarsus, metatarsus, and toes. The tarsus consists of seven small bones placed between the leg and metatarsus; they are called astragalus, os calcis, os naviculare, os cuboides, and three ossa cuneiformia. The astragalus is the upper bone of the foot; it is large and articulated both with the tibia and the fibula supporting the tibia, and being supported itself by the os calcis. This last is of a very irregular figure, and is the largest bone of the foot. Behind it is formed into a considerable tuberosity called the heel. On the internal surface of the os calcis there is a considerable sinuosity which affords a passage to a tendon, and to its hind part a very strong tendinous chord is attached called the tendo Achilles. The navicular bone is concave at its posterior part so as to receive the astragalus; anteriorly it is connected with the cuneiformi bones, and laterally with the os cuboides, which last, as its name imports, is of cube shape and is connected with the heel bone; it also supports the two last bones of the metatarsus, and joins the third cuneiform and the navicular bone. 133. Each of the cuneiform bones resembles a wedge. They are placed next to the metatarsus, are united to the navicular bone, and support the three first metatarsal bones. The whole of these bones in connection form the upper part of the foot, the mass being convex above and concave underneath. 134. The metatarsus is composed of five bones; the first of these, which is much larger than the rest, supports the great toe; the others are pretty nearly alike in size, and correspond with the other toes, the junction of them all being at one end with the cuneiform bones and os cuboides, and at the other with the toes. The bodies of these bones are somewhat triangular. 135. The toes consist of three bones, excepting the great toe which is made up of only two; the three bones are called phalanges. 136. There are several bones called sesamoid, occasionally found among the bones of the toes; they are usually situated on the joints of the great toe; their size is ordinarily about that of a small pea. BONES OF THE UPPER EXTREMITIES. 137. These hang from the superior parts of the sides of the chest and are composed of the bones of the shoulder, arms, fore-arm, and hand. 138. The shoulder is made up of two bones, viz. the clavicle or collar-bone, and scapula or shoulder-blade; these are united together immediately over the top of the os humeri, and thus form what is properly termed the shoulder. 139. The clavicle is a long roundish bone, shaped like the letter S, and situated obliquely in the upper and lateral part of the chest. 140. The scapula, or blade-bone, is triangular, and placed in the upper and lateral part of the back. Its anterior and internal surface is irregularly concave; its posterior and external surface is convex, and divided into two unequal parts by a ridge or process called the spine of the scapula; the fore part of this process is named the acromion, to which the clavicle is fixed. Near this process is another called coracoid, and close to this is a semicircular niche or groove for the passage of blood-vessels. 141. The shoulder joint is formed by the large round head of the humerus and the shallow articular cavity of the scapula. 142. The arm consists of one long bone, the humerus just mentioned which occupies the space between the junction of the clavicle with the scapula, and the fore-arm. It is a long cylindrical bone, thickish at its ends, and distinguished into body and extremities. The humerus is connected to three bones, with the scapula, the radius, and the ulna. 143. The fore-arm is made up of two bones, the ulna and radius; the first forms the internal and posterior, and the second the external and anterior part. The ulna, at its upper extremity, has one large process named olecranon, and a small process on the fore part; and on one side between these is also a small cavity which receives the upper end of the radius. At the lower end of the ulna is a process called styliform, and a round head which is received into the radius. 144. The radius is received at its upper end into the ulna. A little below its head a large tubercle is found. There is likewise a thin edge into which the transverse ligament is fixed, which arises from the ulna. The radius is connected to the humerus, the ulna, and the carpus. 145. The carpus, metacarpus, and fingers, compose the bones of the hand; as the tarsus, metatarsus, and toes, do those of the feet. Each hand has thus twenty-six bones. 146. The carpus or wrist is situated between the fore-arm and metacarpus. It is composed of eight bones, which lie close to one another in a double row, one of which is superior, the other inferior; in the superior row are the os naviculare or scaphoides, os lunare, os cuneiforme, and os orbiculare or pisiforme. In the lower row are the trapezium, trapezoides magnum, and cuneiform bones. All these bones are convex towards the back, and slightly concave towards the palm of the hand; they hear some resemblance to the names given to them, but are not easily known when seen separately. 147. The metacarpus consists of four bones, which sustain the fingers, and one shorter bone for the thumb. 148. The fingers are situated at the inferior extremity of the metacarpus, and consist of the thumb and four fingers, properly so called. These last consist of three separate parts, called phalanges; the thumb is only divided into two phalanges. Each phalanx of the fingers is broadest at its upper extremity, and formed into a superficial cavity; the body or middle part is convex outwardly and concave anteriorly. The lower extremity is rounded. OF LIGAMENTS, CARTILAGES, &c. For the general structure and constitution of ligaments, see § 66 et seq. 149. Ligaments of the head. The condyle of the under jaw has a capsular ligament, which is connected with the temporal bone. There is also a lateral ligament extending between the posterior maxillary foramen, and the petrous portion of the temporal bone. Within the joint there is an interarticular cartilage. A general capsular ligament surrounds the condyles and connects the skull with the cervical vertebræ. Between the occipital bone and upper part of the tooth-like process of the second cervica vertebra, there is a perpendicular ligament. There are two ligaments also which have been named lateral; these arise from each side of the tooth-like process, and are inserted into the oсcipital bone before the condyles. There is also a circular ligament arising from the edge of the spinal foramen, and inserted into the edge of the foramen magnum. 150. Ligaments of the vertebra. There are tendinous extensions between the spinous and transverse processes of the vertebræ; and a strong fibrous ligament runs along the fore parts of the vertebræ, which becomes broader as it approaches the sacral bone; it is formed by a number of intervertebral ligamentous fibres: between the spinous processes of the neck, an elastic yellow |