PalcBontology. 



167 



restricted to the Ruminants, and appear under three 

 different forms or types -namely, solid, as in antelopes ; 

 hollow, as in sheep ; and deciduous, as in deer. Now, 

 in each of these divisions we have a tolerably complete 

 palseontological history of the evolution of horns. 

 The early ruminants were altogether hornless (Fig. 60). 



Fig. 60.— Skull of Oreodon Culbertsoni. (After Leidy.) 



Then, in the middle Miocene, the first antelopes ap- 

 peared with tiny horns which progressively increased in 

 size among the ever-multiplying species of antelopes 

 until the present day. But it is in the deer tribe that we 

 meet with even better evidence touching the pro- 

 gressive evolution of horns ; because here not only 

 size, but shape, is concerned. For deer's horns, or 

 antlers, are arborescent ; and hence in their case we 

 have an opportunity of reading the history, not only 

 of a progressive growth in size, but also of an increasing 

 development of form. Among the older members of 

 the tribe, in the lower Miocene, there are no horns at 



