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THE STRUCTURE OF THE HOESE 



large cavities containing only air, one on each side, 

 situated at the base of the skull behind the pharynx, 

 and connected with the Eustachian tubes (the canals 

 which convey air to the internal chamber of the ear), 

 and which in the most approved works on veterinary 

 anatomy are said to be 1 found only in solipeds.' 

 Exactly similar pouches exist in the tapir, but I am not 

 aware whether they have as yet been looked for in the 

 rhinoceros. They have been supposed to have some 

 use in connection with the function of hearing ; but it is 

 possible they may rather be classed with the numerous 

 large air sinuses found within the bones of the head of 

 the horse, in common with most other mammals, the 

 object of which is evidently to give increased volume 

 without increased weight, and thus to furnish wide 

 surface for the attachment of muscles and for the sup- 

 port and protection of various organs situated within 

 the head. 



It has been pointed out that in the artificial con- 

 ditions under which some domestic horses live, these 

 pouches may become sources of trouble and even 

 danger. As they communicate with the nasal chambers 

 by slit-like orifices, when the horse sniffs air is drawn 

 into them. Should this occur when the animal is 

 feeding in a manger or nose-bag, or the food is dusty, 

 minute particles may enter the pouches and set up 

 inflammation, or give rise to the formation of solid 



