754 



ARTIODACTYLS 



xxxi. 7- 



ment of the feeding system described on p. 743, with loss of the upper 

 incisors and often also of the canines, development of selenodont 

 molars, and of a four-chambered stomach. In the legs only two digits 

 are functional, though traces of others may be found. Besides loss of 

 the extra carpal and tarsal bones there is fusion of those that remain 

 and in particular of the navicular and cuboid. Protection is afforded 

 mainly by swift running and keen senses, but in nearly all ruminants 

 also by antlers or horns on the head. 



This definition will not quite cover all members of the groups. The 

 chevrotains keep so many primitive features that although they are 



Fig. 500. Chevrotain, Tragulus. (After Beddard, Cambridge Nat. Hist., Macmillan & Co.) 



certainly related to the ancestors of the other ruminants it would be 

 almost as easy to class them with the camels. This is another case 

 where it is difficult to decide whether to make horizontal or vertical 

 classificatory divisions; any system is bound to be arbitrary. 



8. Chevrotains 



The deerlets or mouse-deer of Africa and Asia (Fig. 500) are peculiar 

 little creatures, only a foot high, with more external resemblance to a 

 rodent than to modern deer. In some features they show suggestive 

 similarity to the pigs. There are no horns, but the upper canines are 

 large and tusk-like. The upper incisors have been lost and the molars 

 are selenodont, but the stomach has only three chambers. The feet 

 have four, hoofed digits in each limb, and although the two main 

 metatarsals are fused to form a cannon bone the metacarpals are still 

 partly separate. The navicular, cuboid, and external cuneiform make 

 a single bone, this being a 'diagnostic' ruminant character. The 

 placenta is diffuse, as in camels. The individuals live alone in the 

 forests, pairing only for breeding. 



In many of these characteristics the chevrotains show signs of 



