26 THE HOUSE. 



The humerus, or upper-arm bone, presents a 

 character not found in any of the existing ungulates, 

 although common in the caruivora — that of a perfora- 

 tion, or foramen above the inner condyle. The two 

 bones of the forearm, are, as in all generalized forms, 

 both fully developed, the ulna being of large size 

 throughout its length. The structure of the wrist, 

 or carpus, is of great interest from its extremely prim- 

 itive condition, each bone of the second row stand- 

 ing directly beneath, and articulating almost entirely 

 and only with, the corresponding bone of the first 

 row. 



The five digits, with their typical number of pha- 

 langes, are completely developed, the third being the 

 longest and strongest. The terminal or ungual pha- 

 langes are expanded, flattened, and rather spatulate, 

 and evidently bore hoofs rather than claws. Each 

 digit has a metacarpal bone and three phalanges, ex- 

 cept the first or pollex (corresponding to the thumb 

 of man), which has but two. 



In the hind leg, the femur or thigh-bone shows 

 considerable evidence of the presence of that project- 

 ing ridge on the outside, known as the third trochan- 

 ter, found in all Perissodactyles, but in none of the 

 Artiodactyle section. The two bones of the lower 

 leg, the tibia and fibula, are distinct and com- 

 plete. 



