ORGANS OF SENSE. 



59 



of the mouth, and opening behind into the pharynx. 

 (Fig. 32.) Their walls are bony, as well as the median 

 septum between them, excepting towards the nares or 

 nasal orifices, where they are cartilaginous and gifted 

 with a certain amount of mobility. Interiorly the nasal 

 fossa3 are lined with a pituitary membrane ; this mem- 

 brane, which is a continuation of the mucous membrane 

 of the mouth, follows all the sinuosities of the nose and 

 penetrates into the cavities or sinuses of the frontal bone 

 and of the superior maxillary bones. In it is spread out 

 the olfactory nerve, whose ramifications collect the im- 

 pressions left by odorous particles. 



A SIDE-VIEW OF THE PASSAGE OF THE NOSTRILS AND THE DISTRIBUTION OF 



THE OLFACTORY NERVE. 4, the olfactory nerve ; 5, the fine divisions of 

 this nerve on the membrane of the nose ; 6, a branch of the fifth pair of 

 nerves. 



The perception of odors takes place almost entirely in 

 the upper part of the nasal fossa3. The nose proper 

 seems to have only a mechanical function in the opera- 

 tion ; it is a receiver, which takes in and arrests the pas- 

 sage of the particles of odorous substances. After acci- 



