THE SKELETON. 61 



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 meta- 

 carpal present in the horse is the third. The reduction of 

 metacarpals in the ancestral 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 

 sesamoid bones are attached on the volar side of the junc- 

 tion 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 ex- 

 cept the Edentata and Ungulata possess five digits. The 

 tapir has four functional digits. The cow, deer, sheep, and 

 pig also have four digits, but only two are functional, the 

 second and the fifth being atrophied and terminating in the 

 small caudo-lateral hoofs which do not touch the ground. 

 The rhinoceros has three functional digits, and the Equidse 

 possess only one digit (Fig. 37), the third, though the 

 atrophied remnants of the second and fourth metacarpals 

 are present as splint bones which do not support phalanges. 



As before stated, the Ungulates are undoubtedly de- 



