THE CEEEBEUM OK PROSENCEPHALON. 



147 



region. Thus the fine ramification of the olfactory neuron of the I order 

 comes into close relation with the dendrites of cells which represent the 

 olfactory neuron of the II order. 



The united terminal ramifications are to be seen, even with low power, 

 on all sections through the apex of the lobe as spherical structures located 

 just beneath the fibers of the olfactory nerve: Glomeruli olfadorii. Prom 

 the olfactory cells of the II order arise new neuraxons, and these pass back- 

 ward toward the area olfactoria. 



The entering and freely decussating Fila olfactoria, the dendrites of 

 the olfactory cells (II order), and the glomeruli together make, at the apex 

 of the lobe, a characteristic picture, which is called Formatio hulbaris. 



In most animals it makes a swelling anteriorly, which is called the 



Fig. 94. — Sagittal section through the Bulbus olfactorius of a frog. 

 (After P. R. y Cajal.) 



Bulbus olfactorius. Sometimes, however, the apex of the lobe is overlaid 

 with the Formatio bulbaris farther back than the visible bulb reaches. 

 Certain amphibians and reptiles especially show a second ovoid bulbar for- 

 mation on the median side of the lobe somewhat back of the usual position. 

 Emerging from the posterior and lateral pole of the spheroidal bulb 

 one always sees the olfactory tract of the II order, — Tradus olfadorius, — 

 which, at first, covers the olfactory lobe, but later- collects in one or more 

 bundles at its outer side and passes posteriorly. This second olfactory 

 bundle is so large that with the unaided eye it may usually be seen as a white 

 bundle. In several teleosts the olfactory bulb is very large and located far 

 forward in the skull. Thence the tracts pass as two great white fasciculi 

 on either side backward into the brain. They might easily be mistaken for 



