248 THE OLFACTOKY MEMBRANE. [BOOK in. 



the cylinder and basal cells, being spherical, while the latter are oval, 

 but also behave in different ways towards various staining and 

 other reagents ; with hsematoxylin and similar staining reagents 

 they stain less deeply than do the nuclei of the cylinder cells. 

 They are obviously of a very different nature ; and since the nuclei 

 of the cylinder and basal cells behave towards reagents very much 

 in the same way as do the nuclei of the cells of the gland ducts, 

 and indeed of the cells in the respiratory portion of the membrane, 

 we may speak of the nuclei of the rod cells as possessing specialized 

 characters. The cell-substance of the rod cells is also of a different 

 nature, more specialized than that of the cylinder and basal cells. 

 The yellowish tint of the olfactory membrane is due to pigment 

 deposited chiefly in the epithelium. 



858. The connective tissue, vascular and lymphatic con- 

 stituents of the dermis present no special > charac ters ; no cushion 

 of modified connective tissue like that seen in the auditory crista 

 or macula is present. The special feature of the dermis is the 

 presence of bundles of fibres of the olfactory nerve arranged in 

 more or less plexiform manner. 



An olfactory nerve fibre is a non-medullated nerve fibre con- 

 sisting of an axis-cylinder, whose fibrillation is at times conspicuous, 

 surrounded by a sheath or neurilemma, and bearing oval nuclei 

 at intervals. Fibres of this kind are bound up by delicate con- 

 nective tissue into small bundles and these by coarser connective 

 tissue into larger bundles. From the olfactory bulb ( 674) 

 numerous large bundles are given off which, piercing the cribri- 

 form plate of the ethmoid bone, run in a plexiform manner in 

 the walls of the nasal chamber in the olfactory region, giving rise 

 to bundles which become successively finer. 



From the bundles lying in the dermis immediately below the 

 epithelium, fibres pass into the epithelium itself, the demarcation 

 between epithelium and dermis being in the olfactory region not 

 very sharply defined. As they pass into the epithelium the fibres 

 break up into fibrils, which running in various directions in a 

 plexiform manner are lost to view in the nuclear layer. Hence 

 the ground substance in which the nuclei of the nuclear layer 

 appear imbedded consists partly of the more or less fibrillar pro- 

 cesses of the numerous rod cells themselves, partly of the more 

 branched processes of the cylinder cells and of the basal-cells, 

 but also and indeed largely of a plexus or at least a tangle of 

 nerve fibrils proceeding from the olfactory nerve fibres. 



Filaments from the fifth nerve are also distributed to the 

 olfactory as well as to the non-olfactory region of the membrane. 



It is contended by many that the fibrils of the olfactory nerve 

 are continuous with the central processes of the rod cells and make 

 no connections with the cylinder cells. From this it is concluded 

 that the rod cells are primarily concerned in the development of 

 olfactory nervous impulses, the cylinder cells acting only as sup- 



