SMELL. 403 



for the distribution of the olfactory nerve. In 

 the Seal this conformation is most fully de- 

 veloped, and the bony plates are here not tur- 

 binated, but ramified, as shown at t in Fig. 385. 

 Eight or more principal branches arise from the 

 main trunk ; and each of these is afterwards 

 divided and subdivided to an extreme degree of 

 minuteness, so as to form in all many hundred 

 plates. The olfactory membrane, with all its 

 nerves, is closely applied to every plate in thig 

 vast assemblage, as well as to the main trunk, 

 and to the internal surface of the surrounding 

 cavity : so that its extent cannot be less than 

 120 square inches in each nostril. An organ of 

 such exquisite sensibility requires an extraor- 

 dinary provision for securing it against injury, 

 by the power of voluntarily excluding noxious 

 vapours ; and nature has supplied a mechanism 

 for this express purpose, enabling the animal to 

 close at pleasure the orifice of the nostril. The 

 hog, which, in its natural state, subsists wholly 

 on vegetable food, resembles herbivorous tribes 

 in the external form and relative magnitude 

 of the turbinated bones ; but they are more 

 simple in their structure, being formed of single, 

 and slightly convoluted plates, without partitions 

 or perforations. In this respect they approach 

 to the human structure, which is even less com- 

 plicated, and indicates a greater affinity with 

 vegetable than with animal feeders. Man, in- 



