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 wdde 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 back of the head of the radius, 

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

 end (Capitulum ulnse) is small and is produced to a l^lunt point (Processus st}'- 



loideus ulnse) . It articulates with the ulnar carpal 

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

 aspect for the radius. 



The caq)us comprises seven bones, three in 

 the proximal row and four in the distal. The 

 numerical reduction in the upper row is appar- 

 ently due to the fusion of the radial and inter- 

 mecUate, constituting a large bone wdiich articu- 

 lates 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 articu- 

 lates with the radius and ulna above and the acces- 

 sory behind; below it rests on the fourth carpal and 

 is prolonged dowmward 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 secontl 

 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, bonc^ articulates with the inner side of the i-adio- 

 intermediate.' 



Five metacarpal bones are present. The first is nuich the shortest; the third 

 and fourth are the longest, and arc about one-fifth longer than the second and fifth. 

 The fifth is the widest at tlie ])roximal 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 num. Each consists of a shaft and two extremi- 

 ties. The shaft is comjiressed from Ix^fore Ixickward. In the third and fourth it 



' This third bono was termed the yiliaeoid in tlie cat by Strauss-Durckcini, and is regarded by 

 some authors as the vestige of an ad(Htional digit, tiie prepollex. 



Fig. 132. — Skeleton of Distal Part 

 OF Thoracic Limb of Dog, 

 External View. 

 Ji, Radial + intermediate car- 

 pal bone; 5, ulnar carpal; 6 , accessory 

 carijal; 7, second carpal; 5, third car- 

 pal; 9, fourth carpal; 10-14, first to 

 fifth metacarpals; /.5, first jihalanx; 

 16, second phalanx; 17, third phalanx. 

 (After Leisering's Atlas.) 



