58 VARIATION 



The bear has five toes, all round, with an additional claw in 

 digit ii behind, which he uses for combing. 



In mice and rats digit I in front is rudimentary. This case is 

 unique because in most instances, where a difference is notice- 

 able, the reduction in digits has proceeded farther behind than 

 before. 



Snakes, especially the large ones, occasionally show external 

 vestiges of hind legs, and internally are frequently found traces 

 not only of the pelvis but likewise of the thigh bone or femur. 1 

 This shows clearly that the snake is a somewhat recent form 

 developed from lizard-like ancestors with limbs, the hind pair of 

 which must have been placed not far from the middle point of 

 the much-elongated body. This view is strengthened by the fact 

 that as a rule but one lung is developed, showing that the body is 

 more slender than formerly. 



Of all studies in digits the most interesting is that of the 

 ungulates or hoofed animals. ' It is also the most profitable, 

 because the majority of our valuable domesticated animals are 

 included in this classification. 



The interest arises from the fact that out of this stock have 

 developed two very different forms of feet, viz. the two-toed (as 

 cattle) and the one-toed (as horses), both evidently having 

 descended from five-toed ancestors, each by a process of its own. 



For example, cattle, sheep, deer, pigs, etc., have two toes (in 

 and iv) well developed into a serviceable foot, with two others 

 (n and v) standing behind, not touching the ground (pigs), often 

 rudimentary (deer), and frequently represented merely by splints 

 (cattle). Occasionally all trace of these digits is lost (giraffe). 



On the other hand, the horse and his kind have but a single 

 toe (in) ; but on either side is a well-developed splint, the re- 

 mains of the second and fourth metacarpals in front and of the 

 corresponding metatarsals behind. They are, however, without 

 functional significance, being attached only above and extend- 

 ing downward with slender shafts and free ends not supplied 

 with digits. 



In this connection it is to be noted that the extinct protohippus 

 of the United States and the hipparion of Europe, both decidedly 



1 Lydekker, Library of Natural History, p. 2535. 



