THE ORGANS OF THE SPECIAL SENSES. 



273 



mitral cells and their processes, by which they are conveyed to the 

 cerebral cortex. In its passage through this tract numerous collat- 



Fig. 256. 



Diagram of the nervous mechanism of the olfactory apparatus. (R. y Cajal.) a, olfactory 

 portion of the nasal mucous membrane ; b, second or glomerular layer of the olfactory 

 bulb j, at the right edge of the molecular layer, which is dotted. The cells of this layer 

 are omitted, c, fourth layer of the bulb, the layer of the mitral cells, two of which are 

 represented ; e, iiti, cells of the fifth or granular layer ; d, olfactory tract ; g, cerebral cor- 

 tex ; h, neurite from a mitral cell, giving off a collateral to the dendrites of a pyramidal 

 cell in the gray matter of the brain ; /, pyramidal cells of the olfactory tract ; j, collateral 

 from a mitral neurite passing, recurrently, into the molecular layer ; I, centrifugal neurite 

 from the cerebrum. 



eral and association-tracts may be influenced in a manner too com- 

 plicated to be readily followed. 



Fig. 257. 



Diagram of the distribution of the auditory nerve within the mucous membrane of the crista 

 acustica. (Niemack.) The bodies of the hair-cells are dotted. Between them are the 

 cells of Deiters, the nuclei of which are shown below the hair-cells. The nervous fila- 

 ments are distributed between these cells. 



4. Hearing. — The acoustic nervous apparatus resembles somewhat 

 that which subserves the sense of touch. The receptive portion consists 



18 



