190 



PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



The former is supplied by a branch of the fifth pair of 

 nerves (Fig. 122, «), which are the nerves of common 

 sensation for the face ; the latter is supplied by the first 

 pair, or olfactory nerve. The former lies along the floor 

 of the cavity and passes directly to the throat ; the lat- 

 ter lies above the general passage to the throat and 

 lungs. The function of the former is breathing, of the 

 latter is smelling. Each of these have connections with 

 the other cavities, the former with cavities in the cheek 

 bones, the latter with cavities in the frontal bones over 

 the brows. Inflammation sometimes extends from the 

 nostrils into these cavities. 



Smelling. — The olfactory lobes rest directly on the 

 cribriform plate of the ethmoid, which here forms a part 

 of the floor of the 

 cranium. It sends 

 out a large number 

 of nerves through 

 the holes of the 

 colander directly 

 down and into the 

 nostrils, and these 

 ramify over its 

 upper chambers 

 and their terminal 

 bulbs are exposed 

 on the surface (Fig. 

 122). Particles of 

 odoriferous sub- 

 stances are carried by the air current, and, coming in 

 contact with the olfactory terminals, produce the sen- 

 sation we call smell. The peculiar form of the terminals 

 sensitive to odors is shown in Fig. 123. 



Any sensation may be involuntary or voluntary. 

 Thus seeing may be involuntary, but looking is voluntary. 



Fig. 123. — Nerve terminals of the olfactory 

 nerves : ol/c, olfactory cells ; olfnf, olfac- 

 tory nerve fibers ; epc, epithelial cells. 



