THE NOSE. 783 



The nervi olfactorii, on the other hand, in Man and in other Mammalia, 

 even in the main trunks given off from the olfactory bulb, present no 

 white medullated fibres at all, but are wholly constituted of pale, 

 slightly granular flattened fibres, 0-002-0-003 of a line wide, with 

 elongated nuclei, which are closely adherent and retained in connection 

 by common sheaths of connective tissue, which are somewhat thicker 

 and therefore whiter in the rami ad septum. With respect to the 

 origin of these fibres, which very closely resemble the embryonic nerve- 

 elements, whether they are derived from the olfactory bulb, or from the 

 cerebrum itself, has by no means been as yet ascertained in Man, or in 

 other Mammalia, although, from the observations of Leydig in the 

 "Plagiostomata," ("Beitrage," p. 34, Tab. L, fig. 6), it is probable 

 that the former is the case. The termination of these nerves is yet 

 more doubtful. This much is readily seen, that the nervi olfactorii, in 

 their course in the mucous membrane of the olfactory region, are gra- 

 dually attenuated as they descend, in consequence of numerous divi- 

 sions at acute angles, and form a plexus which may also, in Mammalia, 

 be traced almost throughout the olfactory region ; but shortly before 

 reaching its border, these plexuses are always lost to sight, nor is any 

 other indication of terminal branches presented; so that, as regards 

 the main fact, I remain quite in the dark. At present it appears to me 

 most probable that the terminal distribution takes place throughout the 

 non-ciliated region, and above all at its border ; at any rate I have 

 never yet been able to detect the filaments of the olfactory nerves in 

 the ciliated epithelium, although they can be traced down to twigs of 

 the size of 0-005-0-01 of a line. I have not seen the ganglion-globules 

 on the inner surface of the finer plexus mentioned by Valentin (" Ncr- 

 venlehre," p. 303), and the rather strange-looking " glands of Bow- 

 man," might have been mistaken for such bodies. 



In the investigation of the olfactory organ, the chief difficulty arises 

 from the softness of the epithelium, and on this account a solution of 

 albumen, or humor vitreus, only should be employed to moisten it. 

 Vertical sections in detached portions of the mucous membrane, are 

 best made with the scissors ; and the edges of folds not unfrequently 

 afford good sectional views. The mucous glands, are found in sections ; 

 those of Bowman on teasing out the structure. Chromic acid cannot 

 be recommended for the olfactory nerves : teasing out the membrane is 

 the most suitable mode of proceeding ; as well as the compression of 

 fresh preparations or of preparations moistened with soda or acetic 

 acid ; lastly, the examination of mucous membrane macerated in water, 

 in which the nerves are preserved for a long time. 



