THE OLFACTORY MEMBRANE 



229 



down to the corium. 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 perhaps in some 



FIG. 2C6. CELLS AND TERMINAL NERVE-FIBRES OF THE OLFACTORY REGION. 



(Highly magnified.) 



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

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

 into fine hairs ; rf, their central filaments. 



mammals, it bears fine stiff hairlike filaments (e). The proximal or vari- 

 cose process becomes lost amongst the plexus of olfactory nerve-fibrils at 

 the base of the epithelium, and is believed to be connected with a fibril. 

 These cells have accordingly been termed olfactory cells. 2. Long colum- 

 nar epithelium cells (a), with comparatively 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 

 regardednot as sensory epithelium-cells, but merely as serving to support 

 the proper olfactory cells ; but, according to Exner, they are also con- 

 nected with the olfactory fibres, and there is no sharp distinction 

 between them and the bipolar cells. 3. Tapering cells are present, 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. 



The corium of the olfactory mucous membrane is also very thick 

 (fig. 267). It contains numerous blood-vessels, bundles, of the olfactory 

 nerve-fibres (which are non-medullatedj, and a large number of serous 



