132 NERVOUS SYSTEM OF VERTEBRATES. 



ticum and forms what is known as the cerebellar crest. This cor- 

 responds to the molecular layer of the cerebellum of higher forms. 

 The inner portion of both cerebellum and acusticum is composed 

 of large and small cells and corresponds to the combined granular 

 and Purkinje cell layer of higher forms. 



The small cells are vastly more numerous in the cerebellum 

 than in the acusticum and the small bodies of the cells closely 

 packed together suggest the names granule cells and granular 

 layer. The great majority of these cells are very small, have from 

 one to three short dendrites with small claw-like branches and 

 give rise to extremely fine neurites. These are the granule cells 



Molecular 



layer 



Granular 



layer 

 Tr. tecto- 

 cerebellaris 



Tuberculum 

 acusticum 



Spinal V tract 

 Secondary gustatory 



tract 

 Tr. bulbo-tectalis " ^^fj^^^^ ~ Tr. tecto-bulbaris 



FIG. 65. A transverse section of the brain of the sturgeon at the level of the V 

 nerve. 



in a strict sense. Their neurites turn toward the outer surface 

 of the cerebellum or acusticum, as the case may be, and run 

 parallel with the surface, forming the molecular layer. In most 

 forms these fibers bifurcate on entering the molecular layer, 

 one branch running forward and one backward. A considerable 

 part of the neurites of granule cells in the cerebellum pass to the 

 opposite side through the roof, forming the superior commissure 

 of the cerebellum. The larger part of the molecular layer fibers 

 end within the cerebellum; the smaller part, consisting of both 

 crossed and uncrossed fibers, pass caudally in the cerebellar crest 



