200 



SKELETON OF THE DOG 



Olecranon 



Processus anconaeus 



■ Semilunar notch 

 ^ Fovea capiluli 



^%^- 



Shaft of ulna- 



Interosseoiis- 

 space 



Shaft of 

 radius 



is produced to a blunt point (Processus styloideus ulnae). It articulates with the 

 ulnar carpal distally, and has a convex facet on its dorso-medial aspect for the radius. 

 The proximal end of the radius unites with the shaft at six to eight months, the 

 distal at about one and a half years of age. The olecranon and the distal end of the 

 ulna fuse with the rest of the bone at about fifteen months. 



The carpus comprises seven bones — three in the proximal row and four in the 

 distal. The numerical reduction in the proximal row is apparently due to the 

 fusion of the radial and intermediate, constituting a large bone (radio-intermediate) 



which articulates with almost all of the 

 distal surface of the radius and with the 

 bones of the distal row. It projects promi- 

 nently on the volar surface of the carpus. 

 The ulnar carpal is long; it articulates with 

 the radius and ulna above and the acces- 

 sory behind; below it rests on the fourth 

 carpal and is prolonged downward to ar- 

 ticulate 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 car- 

 pal is the smallest bone of the lower row; 

 it articulates with the second carpal later- 

 ally and the first metacarpal distally. The 

 second carpal is wedge-shaped, the base be- 

 ing posterior; its proximal surface is con- 

 vex, and its distal is concave and rests on 

 the second metacarpal. The third carpal 

 is somewhat like the second; its distal sur- 

 face is concave and articulates chiefl}^ with 

 the third metacarpal. The fourth carpal 

 is the largest of the row; it articulates with 

 the fourth and fifth metacarpals. Two 

 small bones or cartilages may be found on 

 the volar surface at the junction of the two 

 rows, and a third small bone articulates 

 with the medial side of the radio-inter- 

 mediate.^ 



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 distally; 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 ex- 

 tremities. 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 



'The third bone was termed the phacoid in the cat by Strauss-Durckeim, and is regarded 

 by some authors as the vestige of an additional digit, the prepoUex. 



Styloid process^ 

 of ulna 



Carpal articular 

 surfaces 



Fig. 220.- 



-Left Raditjs and Ulna of Dog; Medial 

 View. 

 a, Rough area for attachment of biceps brachii 

 and brachialis muscles; b, groove for tendon of exten- 

 sor carpi obliquus. 



