758 



ARTIODACTYLS 



XXXI. II 



be a condition similar to that of Miocene cervids, whereas others 

 believe that the bony core is of dermal origin, as in bovids, fusing 

 later with the frontal. In the okapi there is a rudimentary keratinous 

 horn at the tip. The lateral digits are completely absent and the legs 

 are very long; the whole structure is specialized to carry the great bulk 

 on the fore-legs, the head and neck balancing the weight of the body 

 and the hind-legs being used mainly for propulsion. In walking the 

 fore- and hind-legs of one side move together; since the weight is 

 balanced on the fore-legs there is no use of the tripodal method of 



Fig. 504. Deer, Cervus. (From life.) 



movement that is usual in quadrupeds. This is an extreme develop- 

 ment of the type of vertebral organization in which the weight-carry- 

 ing beam ends in the middle of the back, there being a small number 

 of ribs, so that the hinder part of the column functions as an upper 

 segment of the hind limbs and the extensor muscles of the back aid in 

 propulsion. The long neck makes it possible to balance the great 

 weight on the fore-legs, and is of use not only for reaching high 

 branches but also as a look-out among the long grasses. The rare 

 Okapia (Fig. 506), discovered in 1900 in the Belgian Congo, is a form 

 with shorter legs and neck, very similar to *Palaeotragas and other 

 Pliocene animals, all possessing small horns. Other lines (*Sivatherinm) 

 acquired a pair of large non-deciduous horns, a course of evolution 



