oGO THE SENSORIAL FUNCTIONS. 



In carnivorous quadrupeds the structure of these 

 houes is still more intricate, and is calculated to 

 ati'ord a far more extensive surface for the distri- 

 bution of the olfactory nerve. In the Seal this con- 

 formation is most lidly developed ; and the bony 

 plates are here not tuibinated, but ramitied, as 

 shown at t, in Fig. ."iHS. 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 })lates. The olfactory membrane, 

 with all its nerves, is closely applied to every plate 

 in this vast assemblage, as well as to the main 

 trunk, and to the internal surface of the surround- 

 ing cavity ; so that its extent cannot be less than 

 120 square inches in each nostril. An organ of 

 such exquisite sensibility requires an extraordinary 

 provision for securing it against injury, by the 

 power of voluntarily excluding noxious vapours ; 

 and nature has supplied a mechanism for this ex- 

 press purpose, enabling the animal to close at plea- 

 sure the oritice of the nostril. 



The Ho^-, 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 complicated, 



be useful to this exceedingly fleet animal by facilitating its breathing, 

 while it is exerting its utmost speed; for the expansion of the 

 nostrils opens also these posterior cavities, the sides of which, being- 

 elastic, remain dilated. (Journal of the Asiatic Society, Feb. 1832, 

 p. 59.) 



