SMELL. 399 



useful in enabling them to discover their natural 

 food at great distances. 



The cavity of the nostrils, in all terrestrial 

 vertebrated animals, is divided into two by a 

 vertical partition ; and the whole of its internal 

 surface is lined by a soft membrane, called the 

 Schneiderian memhrane* which is constantly 

 kept moist, is supplied with numerous blood- 

 vessels, and upon which are spread the ultimate 

 ramifications of the olfactory nerves. The rela- 

 tive magnitude of these nerves is much greater 

 in carnivorous quadrupeds than in those which 

 subsist on vegetable food. In quadrupeds, as 

 well as in man, these nerves are not collected 

 into a single trunk, in their course towards the 

 brain, but compose a great number of filaments, 

 which pass separately through minute perfora- 

 tions in a plate of bone, (called the ethmoid hone)^ 

 before they enter into the cavity of the skull, 

 and join that part of the cerebral substance with 

 which they are ultimately connected. 



The surface of the membrane which receives 

 the impressions from odorous effluvia, is con- 

 siderably increased by several thin plates of 

 bone, which project into the cavity of the nos- 

 trils, and are called the turbinated hones. These 

 are delineated at t, t, in Fig. 382, as they appear 



* It has been so named in honour of Schneider, the first ana- 

 tomist who gave an accurate description of this membrane. 



