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decussates in the floor of the mesencephalon as a crossed connection 

 between the acustic center and the nucleus of the N. oculomotorius. 

 This is accepted by Tretjakoff and the tract which decussates behind 

 the level of the N. acusticus he calls the tractus octavo-motorius 

 posterior. He thinks that this makes connections with the posterior 

 group of Miillerian cells. Upon reviewing this subject I am able to 

 confirm the description given by Schilling that the spindle cell fibers 

 which decussate below the level of the N. acusticus turn caudad and 

 pass down into the spinal cord. These fibers are conspicuously thick 

 (about half as thick as the fibers of the giant Miillerian cells) and 

 were included by Ahlborn among the Miillerian fibers. They pass 

 down diffusely scattered in the ventral and lateral white matter. I do 

 not find anything to indicate that these fibers are related to the 

 Miillerian cells, nor do I see that Tretjakoff has given any evidence 

 for that view. If these fibers end in the motor columm of the cord 

 they are homologous with the descending vestibulo- spinal tract in 

 higher forms. I think this hypothesis very probable, the more so as 

 the ascending fibers from part of the spindle cell nucleus go to the 

 nucleus of the N. oculomotorius. 



It is to be noted that certain fibers which arise from the deep 

 cells of the acusticum grow thick as they enter the ventral decussation 

 and it is entirely possible that some of these fibers belong to the 

 vestibulo-spinal tract also. Schilling, indeed, speaks of the cells of 

 origin of the vestibulo-spinal tract as multipolar cells. I no longer 

 believe that the spindle cells form a nucleus peculiar to cyclostomes. 



Edinger (1908) has identified the vestibulo-spinal tract with the 

 Miillerian fibers in fishes, but he derives the fibers from the giant cells 

 and then identifies Deiters' nucleus with a part of these giant cells. 

 As this is equivalent to placing Deiters' nucleus in the ventral motor 

 column in the brain of fishes, I can not accept this interpretation. 

 I am as strongly as ever incHned to the view that the Miillerian cells 

 and fibers are peculiar to fishes, are perhaps vestigeal in character 

 and that they are not to be compared with any characteristic or 

 highly developed structure in higher vertebrates. The vestibulo-spinal 

 tract arises from the vestibular center (not from giant cells nor from 

 the ventral column) and it is important to distinguish this from the 

 Miillerian fibers. 



According to Tretjakoff the only fibers which end upon the 

 spindle cells are those of the acustic nerve. I have examined the matter 

 again and can affirm positively that in Lampetra the lateralis fibers 

 have this mode of ending also. Indeed, the lateralis fibers are the 



