SMELL. 



401 



great an extent of surface as possible within 

 the confined space of the nasal cavity. This 



turbinated, or spiral shape, chiefly characterises 

 these bones among herbivorous quadrupeds : 

 in the horse, for example, the turbinated 

 bones are of a large diameter, and extend the 

 whole length of the prolonged nostrils. Their 

 structure is exceedingly intricate ; for while 

 they retain externally the general shape of an 

 oblong spiral shell, they are pierced on all 

 their internal sides with numerous perforations, 

 through which the membrane, together with the 

 fine branches of the nerves, passes freely from 

 one side to the other. The cavities resulting: 

 from the convolutions are intersected by un- 

 perforated partitions of extraordinary tenuity, 

 serving both to support the arches of bone, and 



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