NOSE 



485 



minates in a variety of ways. It may end in a small knob-like swelling, 

 or in a single slender spine; sometimes the terminal knob sends out a small 

 cluster of divergent olfactory hairs or spines. Basally the olfactory cells 

 pass directly into the axis cylinders of the olfactory nerves (Fig. 492). 

 Thus they are ganglion cells, their basal processes being neuraxons. Cells 

 intermediate between the olfactory and sustentacular forms may be found, 

 and these are doubtless imperfectly developed sensory cells. At the free 

 surface of the olfactory epithelium there are terminal bars, and small 

 projecting strands of mucus, sometimes suggesting cilia (Fig. 490, s). 



Central ependymal 

 cells. 



Fibers of the olfac- 

 tory tract. 



Mitral cells. 



Glomer 



Olfactory nerves. 



Olfactory fibers in 



the nasal mucous 



membrane. 



Olfactory cells. 



FIG. 492. CHIEF ELEMENTS OF THE OLFACTORY BULB. (Gordinier, after Van Gehuchten.) 



The mucus, which is the product of the sustentacular cells, may appear to 

 form a continuous superficial membrane (Fig. 491). Near the tunica 

 propria there is a network of so-called "basal cells" (Fig. 491). 



The tunica propria is composed of fibrous tissue and fine elastic 

 fibers, associated with many connective tissue cells. In some animals 

 (for example, the cat) it forms a structureless membrane next to the epi- 

 thelium. It surrounds the numerous olfactory glands (Bowman's glands). 

 In man these consist of excretory ducts extending through the epithelium, 

 and of branching gland bodies beneath. They have the appearance of 

 serous glands, but sometimes contain mucus, generally in small quantities. 

 They are found not only in the olfactory region, but also in the adjoining 

 part of the respiratory region. 



