THE HEAD AND NECK 



133 



great exertion, begin to pant, and require an additional 

 quantity of air to that which is ordinarily taken in by 

 the nose, the mouth comes to the aid of that channel, 

 and is widely opened ; but the horse under the same 

 circumstances can only expand the margins of the nostrils, 

 for which action there is a very efficient set of muscles, 

 acting on the cartilaginous framework which supports 

 them and determines their peculiar outline. The varia- 

 tions in the form and amount of dilatation of the nostrils 

 give great character and expression to this part of the 

 horse's face. 



Immediately within the margin of the upper part of 

 the nostril is a structure of very considerable interest, 

 which is generally supposed to be peculiar to the horse 

 and its immediate allies, the use of which is entirely 

 unknown. It is a blind pouch, three to four inches 

 in depth, conical in form, though slightly curved, and 

 lying in the cleft seen in the dried skull between the 

 nasal and premaxillary bones. It is a diverticulum 

 from the nasal passage, with which it freely com- 

 municates below, and is lined by a continuation of 

 the same smooth mucous membrane which lines the 

 passage. In veterinary anatomy it is called the ' false 

 nostril.' 



If this were all we knew about this organ it would 

 be- unsatisfactory enough, but it immediately acquires 

 interest when we learn that in the tapir a similar struc- 



