Chap. IX.] 



FEET OF UNGULATA. 



355 



connected with the lateral digits gradually dis- 

 appear. 



In the series of Artiodactyla (even-toed forms) 

 we find, to take the foot, four toes, distinct metatarsal, 

 and distinct tarsal bones (in the pig) ; in the Chevro- 

 tains (Tragtilus), the second and fifth digits are still 

 smaller, and while their metatarsals are distinct, the 

 third and fourth 

 metatarsals have 

 united together, 

 two of the tar- 

 sals have united 

 together, and 

 one of the rest 

 has disappeared; 

 in the musk- 

 deer, as in the 

 true deers, the 

 outer digits are 

 not directly arti- 

 culated with the 

 other bones of 

 the foot, and the 

 outer metatar- 

 sals have, as in 

 them, disappeared ; the musk-deer, however, retains 

 what the deer have lost, the extensor muscle of the 

 fifth digit. 



While the large number of what are really or 

 practically two-toed Ungulates is evidence that this 

 reduction of the digits has not been associated with 

 any diminution in the value of the limbs as locomotor 

 or supporting organs, we have palseontological evidence 

 of the disappearance of a group of even-toed Ungulates 

 who tended to lose their lateral digits. When we ex- 

 amine the carpus of a deer we see that the carpal bones 

 have fused with one another, and have not disappeared 



IE 



Fig. 151. Foot of Anchitherium (A); Hippa- 

 riori (B), and Horse (c). 



ii, in, iv, digits. 



