l82 



NERVOUS SYSTEM OF VERTEBRATES. 



in the olfactory bulb (or ending in it from behind) form the olfac- 

 tory tract. In many fishes and some reptiles the olfactory bulbs 

 are drawn forward some distance from the forebrain so that 

 the olfactory tract is a long cyhndrical structure which contains 

 a slender continuation of the forebrain ventricle. In cyclostomes, 

 amphibia and mammals the bulb is closely applied to the fore- 



FlG. 98. — Cells with short neuritcs in the olfactory bulb of mammals. Schematic 

 figure from Cajal. A , Golgi cell ; 5, cell with peripheral neurite; C, horizontal fusiform 

 cell of the internal plexiform layer; D, cell with horizontal neurite; E and F, 

 periglr merular corpuscles; a, collateral of mitral cell neurite; b, collateral of a small 

 brush cell. 



brain so that the olfactory tract does not run for any considerable 

 distance free from surrounding gray matter. In all cases the fibers 

 of the olfactory tract enter one or other of several groups of cells 

 which collectively should be called the olfactory lobe or area. 



