246 



NERVOUS SYSTEM OF VERTEBRATES. 



brachium decussates in the ventral wall of the mesencephalon, 

 passes through the nucleus ruber and ends in the optic thalami. 

 The nucleus dentatus is concerned chiefly with somatic sensory 

 impulses and is more closely related to the cortex than to the deep 

 nuclei. This indicates a correspondence between this submerged 

 and folded nucleus of the human cerebellum and the portion of 



Cerebellum 

 Tectum 



tecto-bulbaris 



Decussatio veli 



Secondary 



gustatory nuc. 



Rad. mesenc. V 



tract 



| *- Tertiar y gustatory 



Secondary 

 gustatory tract 

 Brachium conjunct! 



Lemniscus system 



FIG. 125. A transverse section through the cerebellum of Necturus. The 

 figure is somewhat diagrammatic in that the whole course of the decussatio veli as 

 drawn does not fall in the same section with the other structures. The actual 

 section from which the outline was drawn inclined forward somewhat, so that it 

 passed through the tectum in front of the velum. The word Cerebellum at the left 

 is placed in the part of the fourth ventricle which extends into the auricular lobe. 



the selachian cerebellum with which the brachium conjunct! vum 

 is connected. In selachians the brachium conjunctivum enters 

 the latero- ventral part of the cerebellum close to the junction 

 with the tuberculum acusticum, a region which is wholly con- 

 cerned with primary sensory and external arcuate fibers. It 

 seems probable that in the evolution of the cerebellum this nu- 



