CHAP. v.J TASTE AND SMELL. 247 



nuclear layer, below which is seen the dermis traversed in various 

 directions by bundles of non-medullated olfactory fibres. And very 

 much as in a macula, the nuclei of the nuclear layer belong to 

 numerous more or less rod shaped or spindle shaped cells, the 

 rod cells. 



A cylinder cell consists of a cylindrical cell body of granular 

 cell-substance, the upper border of which forms part of the free 

 surface of the epithelium, and the lower part of which, after 

 bearing a more or less ovoid nucleus, becomes narrow and ends 

 in an irregular branched less granular process lost to view in 

 the nuclear layer. Near the confines of the respiratory mucous 

 membrane, these cylinder cells bear, in some cases, cilia ; and indeed 

 at the margin of the olfactory membrane, pass into ordinary colum- 

 nar ciliated cells ; but, as a rule, they bear no cilia elsewhere. 



A rod cell consists of a spherical nucleus, surrounded with 

 an exceedingly thin layer of cell-substance, which is prolonged 

 peripherally, as a rod-shaped process directed between the cylinder 

 cells and ending between them at the free surface of the epithelium. 

 In the lower animals, amphibia, the free end bears a fine bundle of 

 delicate hairs, which like cilia are capable of movement, though 

 moving in a peculiarly slow, gentle fashion ; whether these cilia- 

 like processes are present in mammals is not as yet settled. 

 Besides this peripheral process the cell bears at the other pole of 

 the nucleus a central process directed towards the dermis. This is 

 more delicate than the peripheral process, often appears varicose, 

 and has much the appearance of a nerve filament ; it is lost to view 

 in the nuclear layer. In some rod cells the peripheral process is 

 longer than others, and the nucleus accordingly placed deeper 

 down ; some of the nuclei lie close to those of the cylinder cells, 

 others close to or nearly close to the dermis, and some at inter- 

 mediate levels ; in fact the nuclei which make up the thick nuclear 

 layer are the nuclei of rod cells, these greatly exceeding in number 

 the cylinder cells. 



An exception to this last statement should be made in favour 

 of the layer of nuclei lying immediately above the dermis. These 

 are oval not spherical nuclei, and the cell bodies are not in the form 

 of rods but more or less irregularly branched. They have been 

 distinguished as basal cells. 



Among these cylinder, rod, and basal cells which make up the 

 mass of the epithelium, numerous cylinders of flattened cubical 

 cells, surrounding a narrow lumen, pass vertically down from the 

 surface of the epithelium to the dermis. These are the intra-epi- 

 thelial ducts of small tubular twisted glands, generally albuminous 

 but sometimes mucous in character, which lie in the deeper parts of 

 the dermis, and which more simple and smaller than the cor- 

 responding glands in the respiratory nasal membrane, have been 

 called the " glands of Bowman." 



The nuclei of the* rod cells not only differ in form from those of 



