CHAPTER VIII. PLATE VIII.-BONES OF THE ARM. FIG. 1. a, the humerus; the head, b, is a portion of a sphere, and exhibits an example of the ball and socket, or universal joint; c, the hinge-joint, instanced in the elbow ; d, the radius ; e, the ulna. The radius belongs more peculiarly to the wrist, being the bone which supports the hand, and which turns with it in all its revolving motions. The ulna principally belongs to the elbow-joint, for by it we perform all the actions of bending or extending the arm. FIG. 2. a, the humerus: b, shows the connexion of the radius, with C1 the ulna, at the elbow. The mode of articulation at the wrist is seen, Fig. 1. Dd* 329 CHAPTER VIII. PLATE IX.- THE SPINE. FIG. 1. The human spine, so named from the series of sharp processes projecting from the posterior part of the vertebræ. The spine consists of seven vertebræ of the neck, distinguished by the perforations in their transverse processes; of twelve belonging to the back, and marked by depressions for the heads of the ribs; and, lastly, of five belonging to the loins, which are larger than the other vertebræ. FIG. 2. A separated dorsal vertebra: a, the body of the vertebra; b, the ring through which the spinal marrow passes: c, c, the articulating surfaces to which the ribs are united. FIG. 3. The vertebra of a very large serpent, drawn from a specimen belonging to the Anatomy School of Christ Church, Oxford. This figure shows the socket of the vertebra. FIG. 4. The ball or rounded joint, evidently calculated for extensive motion. FIG. 5. A part of the spine of the same reptile; it is exceedingly strong, each bone being united to the other by fifteen surfaces of articulation. |