MAMMALS 



97 



sheath -horned ruminants, pointing out that in these all 

 degrees exist between the complete absence of horns in the 

 females and their equal development in both sexes. Here 

 as in the case of deer we can scarcely doubt that when the 

 horns are present only in the mature males, their presence is 

 associated with fighting habits also confined to the males, 

 but it is more difficult to decide whether the development in 



Fig. 7. The horns and part of the skull of an Ox, to show the relations of bono, skin, and 

 horn-sheatli. The horn of the left side in section. The space between the bony core 

 and horn-sheath is occupied during life by vascular periosteum and skin, and non- 

 vascular living epidermis. From a specimen in the British Museum of Natural History. 



the females is dependent on the practice of similar habits, or 

 is merely due to some change in the course of heredity which 

 is not directly dependent on special habits in the female. 

 Before, however, discussing such questions in detail it is 

 necessary to consider the difference between these horns and 

 the antlers of deer, and to state what reason there is for 

 attributing the former also to mechanical irritation of the 

 frontal bone, or more correctly of its periosteum. 



The peculiarities of horns, then, as distinguished from 



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