502 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



nerve), in order, on the other side of the median line, to reach 

 the auditory nucleus opposite to their origin from the cere- 

 bellum. They thus interlace with both posterior longitudinal 

 fasciculi. 



In virtue of this course, the fasciculi, H', traversing the posterior 

 sections of the internal area of the cerebellar peduncle with the audi- 

 tory fasciculi, 8 3 , interweaving with the anterior sections, would form, 

 in fig. 255, at H, a continuous tract of decussation through the audi- 

 tory nucleus, vin., the whole of which, however, never occurs in one 

 and the same plane of transverse section. A phase of this tract is 

 exhibited in fig. 256, at 8"' vm. 



In their second mode of running, the cerebellar fasciculi, 

 without traversing the internal auditory nucleus, pass through 

 the external nucleus directly forwards, and into the fibrae 

 arcuatae (fig. 255, a) which are all placed in front of the 

 posterior longitudinal fasciculi, but in the raphe' curve round 

 towards the grey floor, and run through the posterior longitu- 

 dinal fasciculus, and behind it into the opposite internal audi- 

 tory nucleus. With the rootlets that run towards the median 

 decussation through the external auditory nucleus transversely 

 into the root of the auditory nerve, these still undecussated cere- 

 bellar fasciculi form a rectangular trellis- work in the fenestrse 

 of which are contained the transverse sections of the descending 

 fasciculi of the internal division of the cerebellar peduncle 

 (fig. 255, H, 257, 8 F C). The innermost fasciculi of the anterior 

 root traverse the ascending fifth nerve, and the lowermost pass 

 into the root, not through the cerebellar peduncle, but imme- 

 diately in front of it. Stilling, deriving it from the auditory 

 nucleus of the same side, considers this last to be the only mode 

 of origin of the auditory nerve. 



The non-decussating portions of the anterior root arise 

 2. From the external auditory nucleus (Clarke, Dean), the 

 large cells of which form a tolerably well-defined and indivi- 

 dualized cluster external to the transverse sections, and extend 

 their processes apparently into the root fibres (fig. 255, 8 4 ). 

 These fasciculi of the root extend themselves beyond the nerve 

 corpuscles into the cerebellum, and indeed, as I have satis- 

 factorily convinced myself, in Man, both through the superior 



