142 



THE NOSE. 



surmounted by a short projection (fig. 159, 2, e) ; according to v. Brunn, this 

 appears in well-preserved specimens to be surmounted by a bunch of fine short 

 hairlets, which are termed the olfactory hairs (fig. 160). Long and fine hair-like 

 processes have long been known to exist on the olfactory cells of amphibia, reptiles, 

 and birds (fig. 159, 1, e). 



In amphibia and fishes the olfactory cells are grouped together in the form ot 

 bud-like organs resembling the taste-buds of the tongue. 



It has been shown by various observers, by aid of the methyl- blue and silver- 

 chromate methods, that the fine varicose central processes of these cells are directly 

 continuous with the fibres of the olfactory nerve, and terminate centrally by 



Fig. 161. DIAGRAM OF THE CONNECTIONS OF CELLS AND FIBRES IN THE OLFACTORY BULB. 



(E. A. S.) 



olf.c.. cells of the olfactory mucous membrane ; olf.n., deepest layer of the bulb composed of the 

 olfactory nerve-fibres, which are prolonged from the olfactory cells ; gl., olfactory glomeruli, containing 

 arborisations of the olfactory nerve-fibres and of the dendrons of the mitral cells ; m.c., mitral cells ; 

 , their axis-cylinder processes passing towards the nerve-fibre layer, n.tr., of the bulb to become 

 continuous with fibres of the olfactory tract : these axis-cylinder processes are seen to give off collaterals, 

 some of which pass again into the deeper layers of the bulb ; n', a nerve-fibre from the olfactory tract 

 ramifying in the grey matter of the bulb. 



dendritic ramifications in the glomeruli of the olfactory bulb (see fig. 161, and 

 Vol. III., Part 1, p. 175). 



Olfactory Nerve. The filaments of this nerve, lodged at first in grooves on 

 the surface of the bones, enter the substance of the Schneiderian membrane 

 obliquely. The nerves of the septum (fig. 162) are rather larger than those of the 

 outer wall of the nasal fossae ; they extend over the upper third of the septum, 

 becoming very indistinct as they descend. The nerves of the outer wall (fig. 163) 

 are divided into two groups the posterior being distributed over the surface of 

 the upper turbinal, and the anterior over the anterior part of the olfactory groove. 

 In the embryo the extent of distribution of the olfactory nerves is relatively 

 greater, but it becomes more limited as development proceeds, and ultimately the 

 actual distribution of olfactory nerve-fibres, to judge by the character of the 

 epithelium covering the membrane, becomes limited to a relatively small tract 

 embracing little but the superior turbinal and a corresponding extent of the septum 

 (v. Brunn). 



