\\lll 



SMKI.I, 



These bony projections, like the rest of the walls of the cavity, 

 are covered by mucous membrane. The epithelium of the 

 mucous membrane in the lower part of each nasal cavity, 

 including the lowest spongy bone, consists of a single layer of 

 tall ciliated cells, like the epithelial cells of the trachea. This 

 is the respiratory part of the nasal chamber, that is, it is the 

 part along which the air chiefly passes in ordinary breathing 

 through the nose. The upper part of the chambers, including 

 the upper and middle spongy bones, is the olfactory part, and 

 the epithelium here is different.<<The epithelial cells are in 



S/t. PL 



FlG. 91. A vertical transverse section 



through the nasal chambers. 

 t>, Cribriform pia: : .?/, septum ; PI, pal- 

 ate ; AH, chamber of upper jaw-bone ; 

 S. T, M.T, I.T, the three turbinal 

 bones. 



FIG. 92. Diagram of olfactory epi- 

 thelium. 



A, The epithelial cells, as they naturally 

 lie, close together ; s, the superficial 

 part ; n, the deeper, nuclear part. 



B, Two ceils separated ; c, a cylindrical 

 cell ; r, a rod cell ; , nuclei. 



more than one layer, and have no cilia ; many of them aie 

 delicate and rod-shaped, and to these latter the branches of 

 the olfactory nerve can be traced. 



By sniffing more air is drawn into the upper parts of the 

 nasal chambers than is the case in ordinary inspiration, so that 

 we sniff when we wish to detect a faint smell. Any odorous 

 particles in the air act on the delicate rod-shaped cells, and 

 impulses pass from them along the olfactory nerves to the brain. 



