76 ELEMENTS OF MAMMALIAN ANATOMY. 



bone consists of a proximal extremity or base, a middle 

 portion or shaft, and a distal extremity or head (Fig. 36). 

 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 are present in most orders. 

 Nearly all the species of every order, except the Edentata 

 and Ungulata, possess five metacarpals. In the pig and 

 hippopotamus there are four metacarpals, in the rhi- 

 noceros 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-bone. Remnants 

 of the second and fifth metacarpals are present in the 

 deer, sheep, and cow, as the small caudo-lateral hoofs 

 indicate. The functional metacarpal present in the horse 

 is the third. The reduction of metacarpals in the ances- 

 tral forms of the horse is shown in figure 35, and will be 

 referred to again in the description of the phalanges. 



Phalanges.- -The cat has five toes or digits on the fore- 

 foot, called pollex, index, medius, annulus, and minimus. 

 Each digit, except the pollex, consists of three phalanges 

 (Fig. 36). The pollex or thumb has only two phalanges. 

 The row of phalanges articulating with the metacarpals 

 is called the proximal, the terminal row the distal, and 

 the remaining row the middle phalanges. Two small sesa- 

 moid bones are attached on the volar side of the junction 

 of each proximal phalanx with the metacarpal. Each 

 distal phalanx has its proximal end produced caudal on 

 the palmar aspect so that its articular surface faces 

 dorsal. The distal phalanges terminate in claws which 

 are retractile. 



The number of digits in the forefoot of Mammalia varies 

 from one to five. Nearly all the species of every order 



