THE SKELETON 



71 



the pollex side, first, second, third, fourth, and fifth metacarpals 

 respectively. Each bone consists of a proximal extremity or 

 base, a middle portion of shaft, and 

 a distal extremity or head (Fig. 37). 

 These bones are curved so as to be 

 slightly convex on the dorsal aspect. 

 The number of metacarpals in 

 mammals varies from one in Equus 

 to five which arc present in most 

 orders. Nearly all the species of 

 every order, except the Edentata 

 and Ungulata, possess five metacar- 

 pals. In the pig and hippopotamus 

 there are four metacarpals, in the 

 rhinoceros three, and in the camel, 

 deer, sheep, and cow two. In the 

 last three forms the metacarpals 

 present are the third and fourth, 

 which in the adult are coalesced 

 into a single bone known as the 

 cannon-hone. Remnants of the 

 second and fifth metacarpals are 

 present in the deer, sheep, and cow, 

 as the small caudo-lateral hoofs indi- 

 cate. The functional metacarpal Fig. 38.— Lateral Aspect of 



. , . , 1 • 1 Left Forelimb of Equus. 



present m the horse is the third, h, Humerus; mz, third meta- 



The reduction of metacarpals in the ^^"p^^^ f ^' ^^^^^^ metacarpal; 



^ p, phalanges; r, radius; s, 



ancestral forms of the horse is sesamoid; sc, scapula; ua, ulna; 



^ ' r /- ^ •^^ ^ <!. navicular; c, lunate; m, tri- 



shown m figure 36, and will be re- q^^tral; n. pisiform; w, capi- 



ferred to again in the description of ^^^^J "• hamate. 

 the phalanges. 



Phalanges. — The cat has five toes or digits on the forefoot, 

 called pollex, index, medins, annulus, and minimus. Each 

 digit, except the pollex, consists of three phalanges (Fig. 37). 



