90 Anatoimy of the Nervous System 



If the observer work back through a series of sections of 

 the olfactory bulb, he will see a new mass of gray matter 

 appear just lateral to the layer of fibres of the medulla of the 

 lateral olfactory gyrus. This enlarges backwards and is 

 found to be the cortex of the lateral olfactory gyrus, on the 

 lateral aspect of which the olfactory tract is seen, while the 

 olfactory bulb extends some distance back along its ventro- 

 medial aspect. 



According to the usual descriptions, the human olfactory 

 tract consists of three parts known respectively as the medial, 

 intermediate, and lateral olfactory striae. The last of these 

 runs into the lateral olfactory gyrus and gyrus hippocampi 

 (which is represented by the pyriform lobe of the rat) ; the 

 intermediate olfactory stria ends in the intermediate olfactory 

 nucleus, which occupies the anterior perforated area of man 

 and includes a vestige of the large tuberculum olfactorium 

 of lower mammals; while the medial olfactory stria is dis- 

 tributed to the subcallosal gyrus (paraterminal body) and 

 septum pellucidum of man, both of which are represented in 

 the septum of the rat. 



The medial olfactory stria is small and diffuse and lies 

 below the surface in the rat, just dorso-medial to the inter- 

 mediate stria, running back over the anterior part of the 

 tuberculum olfactorium. The intermediate olfactory stria 

 is better developed, but runs along the medial aspect of the 

 lateral olfactory stria in the anterior part of the course of 

 this bundle, so that it does not appear as a distinct structure, 

 the two together forming a single conspicuous olfactory tract 

 on the latero-ventral aspect of the brain (PL XXIV.). 



The olfactory tract (lateral olfactory stria only, in its 

 more posterior part) forms a conspicuous band extending 

 back along the ventral surface of the hemisphere for about 

 half the length of the latter, accompanied by the gradually 

 increasing gray matter of the lateral olfactory gyrus. The 

 depression in the surface of the cerebral cortex occupied by 



