380 Miciiost'uric \\.\TOUY or THE 



which allows of the passage of the peripheral hair-bearing ends 

 of the olfactory cells through small spaces. At the lower edge 

 of the epithelium in the region of the forked basal ends of the 

 supporting cells there lie the so-called basal cells. These are 

 conical cells arranged in a row and joined together by proc- 

 esses. Their nuclei form the lowest row in the whole epi- 

 thelial layer. 



The connective-tissue tunica j>roj>ria forms a compact layer 

 under the epithelium. It contains a fine network of elastic 

 fibres, a large number of leucocytes, and a few pigment cells. 

 Numerous glands are also present (Fig. 275). These glandulce 

 olfactories (Bowmann) are simple or branched tubular serous 

 glands. They open on the surface of epithelium by means of 

 narrow ducts lined with flat epithelium. 



The non-medullated fibres of the olfactory nerve passing 

 through the tunica propria toward the bulbus olfactorius are 

 derived from the lower processes of the olfactory cells. On 

 the other hand, there are branches of the trigeminal nerve 

 which end freely in the tunica propria and epithelial layer, 

 and also in the respiratory region. 



The arteries running in the deeper parts of the tunica pro- 

 pria break up into fine branches, which form three capillary 

 systems (Zuckerkandl). One lies deep down in the perios- 

 teum, oue surrounds the glands, and the third forms a network 

 immediately under the epithelium. The veins make up a 

 strongly developed plexus in the deeper parts of the tunica 

 propria. This takes part in the formation of the erectile 

 bodies. 



The lymph-vessels are arranged in a network in the tunica 

 propria. Those of the olfactory region may be injected from 

 the subarachnoideal space; for the olfactory nerve is sur- 

 rounded by a continuation of the membranes of the brain. 



Jacobson's organ is to be regarded in man as a rudimentary 

 structure. It contains no sensory cells. In the lower animals, 

 on the contrary, it is functional, and has the same structure as 

 the olfactory mucous membrane. 



