8 THE AMERICAN NATURALIST. [Vol. XXXV II I. 



lateral metapodials are incompletely ossified. The metacarpals 

 are not fused, while the presence or absence of fusion of the 

 metatarsals is a specific variation. 



The extinct Oligocene genus Protoceras gives us an inter- 

 esting example of the acceleration of the specialization of the 

 hind limbs over the fore, for while the latter have four well 

 developed functional digits those of the former are reduced to 

 two only, with closely applied metatarsals which do not fuse, 

 though strongly tending so to do. The lateral metatarsals 

 are represented by proximal vestiges only. 



In the Pecora or true deer the lateral digits are reduced, 

 being functionless in most genera though sub-functional in 

 Moschus and in Rangifer probably due, in the latter genus at 

 any rate, to the necessity of a broad plantar surface for support 

 on the mossy tundras or on the snow, a condition analogous to 

 that of Hypohippus among the horses. In the deer the lateral 

 metapodials are incomplete, their distal ends always occurring 

 while only in certain genera as Cervus and Cariacus are the 

 proximal extremities also retained. 



The Bovidse exhibit an almost complete reduction of the 

 lateral digits, the dew claws being dermal appendages only, the 

 proximal phalanges being invariably absent, while the final stage 

 of total reduction of the lateral toes is found in the camels, the 

 giraffe, and in Antilocapra. In the Bovidae as well as in the 

 later Camelidae and the other forms mentioned the fusion of 

 the metapodials to form a canon bone is complete. 



In the later camels there is a retrograde descent from the 

 unguligrade to the digitigrade condition, wherein the phalanges 

 lie prone upon the ground, giving the characteristic broad, pad- 

 like foot of the modern camel. 



There are no instances of saltatorial adaptation among the 

 ungulates though some antelope and deer are wonderful 

 jumpers. 



The lemurs among the primates present several instances of 

 saltatorial adaptation, notably in the sub-family Galagininse and 

 in Tarsius, family Tarsiidae ; but here instead of an elongated 

 metatarsus, which has been the rule heretofore, it is the tar- 

 sus which is modified, for the calcaneum and navicular become 



