EARS. 



207 



applying their ears to the sides of their burrows, and 

 Ustening for the sound of the worms. As the external 

 ear of an animal is less solid than the middle ear, the 

 presence of external ears in moles would diminish their 

 ability to hear sounds transmitted through the soil which 

 they inhabit. The more the external ear of an animal 

 approaches an ear-trumpet, in its large size and funnel- 

 shape, the better will it convey sounds that are trans- 



Pliulo 6i/] [M. H. H. 



Fig. 300. — High Occipilal Crest. 



mitted through the atmosphere. Consequently we find 

 comparatively large and funnel-shaped external ears in 

 animals which, like wild asses, zebras, deer and antelope, 

 require well-developed power of hearing, in the struggle 

 for existence. In the following remarks, the term " ears" 

 will, for shortness' sake, be used only with reference to 

 the external ears. In the horse tribe, the largest ears are 

 possessed by the Mountain Zebra (Fig. 310) and Grevy's 

 Zebra (Fig. 301) ; the former being an inhabitant of 



