38o THE INTERMEDIATE PRIMATES 



LE\ EL OF THE MIDDLE OF THE PONS \AROLII (FIG. 1 78) 



Here this structure attains its lull dimensions. It presents the three 

 characteristic pontile layers, the stratum superficiale pontis, the stratum 

 complexum pontis and the stratum profundum pontis. In the complex 

 layer of the pons Varolii opportunity is atlorded to estimate the size and 

 extent of the pontile nuclei (PN) which appear to be considerably larger 

 than in baboon. The pyramidal libers (Py) occupy their usual position 

 in the center of this layer, their bundles being much dispersed by the 

 interposition of nuclear substance and many decussating fibers of this middle 

 layer of the pons. The impression conveyed by the pons and its large nuclear 

 mass is that it belongs to an animal possessed of relatively high coordinative 

 control in its skilled movements. 



Situated between the basis and the tegmentum, as the boundary line 

 between these two, is the mesial fillet (Mf); lateral to the mesial fillet 

 is the lateral lillet (Lf), in the dorsal extremity of which is the nucleus 

 of the lateral fillet. A dense and large bundle of myelinized fibers in the 

 extreme lateral position of the cross section is the middle cerebellar pe- 

 duncle (Mcp), while situated in the dorsolateral angle of the section is a 

 smaller dense bundle of iibcrs which represents the superior cerebellar pe- 

 duncle (Sep). On the periphery over this bundle of fibers is a thin band 

 of myelinized axons, the ventral spinocerebellar tract (Gow) on its way 

 to the vermis of the cerebellum. Interposed between this latter tract and 

 the superior cerebellar peduncle is the tractus uncinatus of Russel (Tur). 

 Ventral to the dense fasciculus forming the middle peduncle, many fibers 

 enter the axis. These axons are the dorsal root fibers of the trigeminal nerve 

 (N5). Their course may be followed through the peduncle into the lateral 

 aspect of the tegmentum where some of them end in relation with the 

 cephalic extremity of the substantia gelatinosa trigemini ( N R). 



