CHAP. XVI.] 



THE OLFACTORY FILAMENTS. 



9 



elementary fibrillae, are nucleated, and finely granula in texture, 

 and are invested with a sheath of homogeneous membrane, much 

 resembling the sarcolemma, or, more strictly, that neurilemma 

 which we figured from the nerves of insects in the former volume, 

 p. 226. These facts we have repeatedly ascertained, and they appear 

 to be of great importance to the general question of the function of 

 the several ultimate elements of the nervous structure, especially 

 when viewed in connexion with what will be said on the anatomy 

 of the retina. We are aware 

 that some anatomists deny the ex- 

 istence of the white substance of 

 Schwann as a natural element of 

 the nerve-fibre in any case,pretend- 

 ing that it is formed by artificial 

 modes of preparation; we hold it 

 to be a true structure; but, how- 

 ever that may be, these nerves 

 never exhibit it, however prepared. 

 They rather correspond with the 

 gelatinous fibres. Now there is no 

 kind of doubt that they are a di- 

 rect contination from the vesicular 

 matter of the olfactory bulb. The arrangement of the capillaries in 

 well-injected specimens is a convincing proof of this, as these vessels 

 gradually become elongated on the nerve assuming a fibrous 

 character as it quits the surface of the bulb; and further, no tubular 

 fibres can ever be discovered in the pulp often left upon the orifices 

 of the cribriform plate after detachment of the bulb. It must be 

 remembered, that a few tubular fibres from the nasal nerve of the 

 fifth here and there accompany the true olfactory filaments, but 

 these only serve to make the difference more evident by contrast. 



Although these nucleated olfactory filaments lie in great abun- 

 dance under the mucous membrane of the olfactory region, we 

 have been quite foiled in our attempts to trace their ultimate dis- 

 tribution in the membrane, and the difficulty is attributable to their 

 want of the characteristic white substance. Their elongated nuclei 

 render the larger branches unmistakeable ; but if these become re- 

 solved at last into fibrous elements, the nuclei cease to be distinct 

 from those of the numerous nucleated tissues which they traverse. 

 In this respect they correspond, in all probability, with the nerves of 

 some of the papillae of the tongue (see vol. i. pp. 436-7) ; and, 

 considering the similarity between the two senses, an argument may 



Olfactory filaments of the Dog: a. In water. 

 6. In acetic acid. Magnified 250 diameters. 



