Each vertebra has a bodv, which is situated anteriorly, and consists of a cy lindrical piece of bone; a perforation be hind this, in which the spinal marrow runs; two superior and two inferior arti culating processes, by which it is joined to the bone immediately above ancl Waw a ; two transverse processes, and onc spi nous process, which, projecting behind. forms a sharp ridge, from which the name of spinc has been applied to the whole column.
The vertebra are divided into three classes, according to their situation : the seven upper °nets are called cervical : of these, the first, that itninediately supports the head, is called the atlas ; and the second, from a remarkable bony process which it possesses, the vertebra dentata. The twelve next are called dorsal verte bra, and are distinguished by having the ribs articulated to them. The five last are called lumbar. These all differ from each other in some circumstances. The most obvious distinction arises from the size : the upper ones are the smallest, and there is a gradual increase as we descend.
The column of the spine, when viewed altogether, is not perpendicular; it stands forwa.rd in the neck, recedes in the up per patt of the back, and projects again in the loins. Holes are left between the bones, for the transmission of the nerves which arise from the spinal marrow.
The sacrum forms the back of the pel vis, and is followed out in front. In form it is triangular, and the base is joined to the last vertebra. It is perforated by a canal, in which the termination of' the me &ilia spinal's is lodged. Its apex has connected to it the os coccygis.
The thorax is formed by the twelve dorsal vertebra, the ribs, and sternum. The ribs arc long, curved, flattened, and narrow bones, attached behind to the dorsal vertebra, both in their bodies and transverse processes, and joined in front to a piece of cartilage. They are twelve in timber, and the seven upper ones, whose cartilages are affixed to the sides of the sternum, are called true ribs ; the five lower ones, the cartilages of which do not reach so far, are called the false ribs.
'flie sternum is a broad and flat bone, placed in the front of the chest. It con sjsts of two pieces of bone, and of a carti lage called the ensiform. The clavicles are articulated towards its upper parts, and the cartilages of the ribs are joined to its sides.
The pelvis is formed by the two ossa innominata, or haunch bones, the sacrum, and os coccygis. The former arc very large and fiat bones, expanded into a broad surface above for the support of' the abdominal viscera, anti the attaclunent of the abdominal muscles, and furnished with large tuberosities below, for the sup port of the body in the sitting position.
Each os innomittatum is divided into the ilium, ischium, and pubes. It is firmly Solite(' to the sacrum behind, and to the ,oppositc bone in front, by the symphisis pubis. The conjoined portions form an arch, called the arch of the pubes. The cavity of the pelvis is much larger in the female than in the male, as it holds the uterus and vagina, in addition to what it contains in the male, and as the fcetus passes through it in parturition.
The Bones of the upper extremity are distributed into those of the shoulder, arm, fore-arm, and hand.
The shoulder contains two; the scapula and clavicle. The former is situated at the upper and outer part of the chest, and is joined to the end of the clavicle.
The humerus is a long and nearly cy lindrical bone, joined by a round head to the scapula above, and articulated with the radius and ulna below.
The fore-arm has two bones ; the ulna, which is joined by a hinge or ginglymus to the humerus ; and the radius, which has a cavity playing npon a rounded head of that bone. The prominent extremity of the ulna, which forms the elbow, is called the olecranon. The hand is di ded into the carpus,'or wrist, the meta carpus, and the fingers and thumb.
The carpus contains eight bones, dis posed in two phalanges, of which the first forms, with the radius, the joint of the wrist, and the second is articulated to the metacarpus.
The bones of the first phalanx are the os scaphoides, lunare, cuneiforme, and pisiforme : those of the second, os tra pezium, trapezioides magnum, and unci forme.
The metacarpus has five bones, and each of the fingers three ; the thumb only two.
In the lower extremity we have the fe mur, the largest of the cylindrical bones in the body. This has a round bead, con tained in a socket of the os innominatum : the great trochanter forms a conspicuous process at the upper and outer part of the bone. Below alias two condyles, which form part of the knee.
The leg has two bones ; the tibia and fibula. A large fiat portion of tbe former, covered only by skin, is called the shin.
Thc foot is composed of' the tarsus, meta tarsus, and toes. The tarsus has seven bones :-1. Astragalus, composing- the ankle, with the lower portion of the tibia and fibula. 2. Os calcis. 3. Os navicu 1 are. 4. Os cuboides. 5, 6, 7. Ossa cu neiformia. The metatarsal bones are five in number, and the bones of each toe are three, except the great toe, which has only two.
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