THE OLFACTORY MEMBRANE. 



277 



very delicate and varicose, looking not unlike a nerve-fibril and extending 

 down towards the cerium. The position of the nuclear enlargement 

 varies, and with it the relative length of the two processes. The distal 

 or free process terminates in a small clear projection, which passes 

 beyond the cuticular membrane ; in amphibia, reptiles, and birds, and 



FIG. 309. CELLS AND TERMINAL NERVE- FIBRES OF THE OLFACTORY REGION. 



(M. Schultze.) (Highly magnified.) 



1, from the frog ; 2, from man ; a, epithelial cell, extending deeply into a ramified process ; 

 b, olfactory cells ; c, their peripheral rods ; e, their extremities, seen in 1 to be prolonged 

 into fine hairs ; d, their central filaments. 



perhaps in some mammals, it bears fine stiff hairlike filaments (e). The 

 proximal or varicose process becomes lost amongst the plexus of olfac- 

 tory nerve-fibrils at the base of the epithelium ; it is connected with 

 one of the fibrils and ultimately passes through the cribriform plate of 

 the ethmoid to end in an arborisation within one of the olfactory 

 glomeruli (see diagram, fig. 285, p. 252). These cells have been termed 

 olfactory cells. 2. Long columnar epithelium-cells (a}, with compara- 

 tively broad cylindrical nucleated cell-bodies placed next the free 

 surface, and long, forked, and branching tail-like processes extending 

 down to the corium. These are usually regarded not as sensory epithe- 

 lium-cells, but merely as serving to support the proper olfactory cells. 

 They are the columnar or sustentacular cells. 3. Tapering cells are pre- 

 sent, at least in some animals, in the deeper part of the epithelium. 

 They rest by their bases upon the corium, and project between the 

 other cells, which they assist to support. 



