40 ELECTRO-PHYSIOLOGY CHAP. 



with a proper stain, as in the transverse sections of Kemak's 

 fibres. But while, from their origin, each of the latter must be 

 regarded as a single axis-cylinder, we are from the same reason 

 compelled to accept each of the fine elementary fibres, or fibrils, 

 within the common sheath of the olfactorius as being in itself 

 a nerve -fibre or axis -cylinder. The peculiar relations of the 

 olfactory fibres to certain spherical structures of the olfactory bulb 

 have long been known, but it is only with the help of recent 

 methods of staining that an explanation of them has become 

 possible. 



It is now known that two processes run out from the spindle- 

 shaped body of each " olfactory cell " one short and directed 

 towards the mucous surface, interpolated between the remaining 

 epithelial cells ; the other, long, fine, and filiform, extending as an 

 olfactory fibre towards the bulb, to end there in a " glomerulus." 

 A number of these extremely fine nerve-fibres are gathered up 

 into coarser bundles (olfactory bundles), which, after a shorter or 

 longer course, pass out of the olfactory mucosa into the olfactory 

 bulb, through the cribriform plate of the ethmoid, and enter the 

 layer of glomeruli. The individual fibres, which are undivided 

 and often varicose, remain of the same breadth throughout their 

 passage from olfactory cell to glomerulus. The fibres begin to 

 branch shortly before entering the glomerulus ; they divide 

 dichotomously several times, and traverse the glomerulus by 

 a somewhat complicated path, until they end freely (5). Often, 

 as described by Eamon y Cajal, Van Gehuchten, and Martin, as 

 well as by Kolliker, " not merely one, but two, three, or several 

 fibres, enter one glomerulus. They all pursue the same course, 

 branching freely (dichotomously) in the glomerulus, and inter- 

 lacing without anastomosis." These terminal ramifications of 

 the olfactory fibres in the glomerulus therefore represent the 

 central endings of the fibres, and in spite of their fine structure 

 they cannot be regarded otherwise than as independent nerve- 

 fibres (axis-cylinders). Each olfactory fibre, or more correctly 

 fibril, thus corresponds with the centripetal process of an " olfactory 

 cell " in the epithelium of the olfactory mucous membrane. The 

 branches of these fibres in the glomerulus interlace, without 

 anastomosing, with other fibres that arise from bifurcation of the 

 processes from the ganglion-cells (prolongations of the so-called 

 "mitral cells"). 



