504 THE SOLIDS. 



" The olfactory filaments are from fifteen to twenty-five in 

 number, and passing through the apertures of the cribriform 

 plate, may be seen invested with fibrous sheaths derived from 

 the dura mater, upon the deep or attached surface of the 

 mucous membrane of the olfactory region. They here branch, 

 and sparingly reunite in a plexiform manner, as they descend. 

 They form a considerable part of the entire thickness of the 

 membrane, and differ widely from the ordinary cerebral nerves 

 in structure. They contain no white substance of Schwann, 

 are not divisible into elementary fibrillas, are nucleated, and 

 finely granular 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 a former volume. These facts we have 

 repeatedly ascertained, and they appear to be of great im- 

 portance to the general question of the function of the several 

 ultimate elements of the nervous structure, especially when 

 viewed in connection with what will be said on the anatomy 

 of the retina. We are aware that some anatomists deny the 

 existence of the white substance of Schwann as a natural 

 element of the nerve fibre in any case, pretending that it is 

 formed by artificial modes of preparation. We hold it to be 

 a true structure, but however that may be, these nerves 

 never exhibited it, however prepared. They rather corre- 

 spond with the gelatinous fibres. Now there is no kind of 

 doubt that they are a direct continuation from the vesicular 

 matter of the olfactory bulb. The arrangement of the capil- 

 laries 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." 

 Physiological Anatomy. 



