The =carpus= comprises seven bones, three in the proximal row and four in the distal. The numerical reduction in the upper row is apparently due to the fusion of the radial and intermediate, constituting a large bone which articulates with almost all of the distal surface of the radius and with the bones of the lower row. It projects prominently on the posterior surface of the carpus. The ulnar carpal is long; it articulates with the radius and ulna above and the accessory behind; below it rests on the fourth carpal and is prolonged downward to articulate with the fifth metacarpal also. The accessory is cylindrical, constricted in its middle and enlarged at each end; the anterior extremity articulates with the ulna and ulnar carpal bone. The first carpal is the smallest bone of the lower row; it articulates with the second carpal externally and the first metacarpal distally. The second carpal is wedge-shaped, the base being posterior; its upper surface is convex, and its lower is concave and rests on the second metacarpal. The third carpal is somewhat like the second; its lower surface is concave and articulates chiefly with the third metacarpal. The fourth carpal is the largest of the row; it articulates with the fourth and fifth metacarpals below. Two small bones or cartilages may be found at the junction of the two rows behind, and a third small bone articulates with the inner side of the radiointermediate.[27] Five =metacarpal bones= are present. The first is much the shortest; the third and fourth are the longest, and are about one-fifth longer than the second and fifth. The fifth is the widest at the proximal end and is slightly shorter than the second. They are close together above, but diverge somewhat below; the first is separated from the second by a considerable interosseous space. They are so arranged as to form a convex dorsal surface, and a concave volar surface, which corresponds to the hollow of the palm of the hand in man. Each consists of a shaft and two extremities. The shaft is compressed from before backward. In the third and fourth it is almost four-sided, in the second and fifth three-sided, in the first rounded. The proximal ends (Bases) articulate with each other and with the corresponding carpal bones. The carpal articular surface formed by them is concave from side to side, convex from before backward. The distal ends (Capitula) have articular surfaces of the nature of a head, but bear a sagittal ridge behind, except the first, which is grooved. [Illustration: FIG. 133.—SECOND AND THIRD PHALANGES OF DOG. _a_, Wing of third phalanx; _b_, coronary ridge; _c_, foramen for digital artery; _d_, ungual surface of third phalanx; _e_, second phalanx; _f_, first phalanx; _g_, elastic dorsal ligaments. (From Leisering’s Atlas.) ]