164 



SKELETON OF THE DOG 



but diminishes in size from above downward. It crosses the posterior surface of 

 the radius from within outward. The shaft is large and three-sided in its upper 

 two-thirds, smaller and more rounded below. Its anterior surface is in general 

 rough. The nutrient foramen is near the proximal end. A vascular groove 

 descends from it and indicates the course of the interosseous artery. The proximal 

 end is relatively short. It is concave and smooth internally, convex and rough ex- 

 ternally. The olecranon is grooved and bears three prominences, of which the pos- 

 terior one is large and rounded. The semilunar notch is wide below and completes 

 the surface for articulation with the trochlea of the humerus. Below it is a concave 

 surface (Incisura radialis) which articulates with the l)ack of the head of the radius, 

 and below this is a fossa, which receives a tuberosity of the radius. The distal 

 end (Capitulum ulnae) is small and is produced to a blunt point (Processus sty- 



loideus ulnae). It articulates with the ulnar carpal 

 below, and has a convex facet on its antero-internal 

 aspect for the radius. 



The carpus comprises seven bones, three in 

 the proximal row" and four in the distal. The 

 numerical reduction in the upper row is appar- 

 ently clue to the fusion of the radial and inter- 

 mediate, constituting a large bone which articu- 

 lates with almost all of the distal surface of the 

 radius and with the l)ones of the lower row. It 

 projects prominently on the posterior surface of 

 the carpus. The ulnar carpal is long; it articu- 

 lates with the radius and ulna alcove and the acces- 

 sory l)ehind; below it rests on the fourth carpal and 

 is prolonged downw^ard to articulate with the fifth 

 metacarpal also. The accessory is cylindrical, con- 

 stricted 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 l)elow. Two small bones or cartilages 

 may be found at the junction of the two rows 

 behind, and a third small l)one articulates with the inner side of the radio- 

 intermediate.^ 



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 extremi- 

 ties. The shaft is compressed from before backward. In the third and fourth it 



' This third bone was termed the phaooid in the cat by Strauss-Diirekeim, and is regarded by 

 some authors as the vestige of an additional digit, the prepollex. 



■^«^ 



16 



Fig. 132. — Skeleton of Distal P.\rt 

 OF Thoracic Limb of Doc:, 

 External View. 

 4, Radial + intermediate car- 

 pal bone; .5, ulnar carpal; 6, accessory 

 carpal; 7, second carpal; S, third car- 

 pal; 9, fourth carpal; 10 -H, first to 

 fifth metacarpals; 15, first jihalanx; 

 16, .second phalanx; 17 , third phalanx. 

 (After Leisering's Atlas.) 



