OF THE NERVUS OCTAVUS. 63 



of these degenerated fibres enters into the medullary capsula sur- 

 rounding the nuclei supra-olivares and para-olivaris of the same side 

 (Plate II fig. 2 str. dors. corp. trap, b, Plate IX fig. 10, B, C, 

 and I)) at is lateral and ventral surface. 



Notwithstanding the loss of fibres in the surrounding of the olivary 

 nuclei of the same side , still an important number of them trans- 

 gresses the raphe dorsally from the described thick fibres, reaches 

 the opposite nucleus para-olivaris and ends there in the medial 

 hilus of the medullary capsula of the opposite nucleus para-olivaris 

 et supra-olivaris. In this way these small fibres represent another 

 set of root-fibres, which also participate in the formation of the 

 system a ventrale nervi octavi. 



In the ,,systema ventrale nervi octavi" therefore may be distin- 

 guished : 2 ly . small root fibres from both roots to the ventral nuclei 

 of the tegmentum on both sides , especially to the nucleus supra -olivaris 

 and the nucleus para-olivaris of the same side. They are situated 

 therein dorsally from the stratum a, described before and form the 

 most ventral of the dorsal layers of the ,,systema ventrale", the 

 stratum b of this system. 



Now , it must be kept in mind , that a well defined corpus 

 trapezoides is only present in its more distal parts. Especially its 

 limitation dorsally towards the tegmentum is difficult. 



Together with the root-fibres , fibres from the ventral auditory 

 nucleus and from the tuberculum acusticuni also participate in the 

 formation of the transversal medullary fibres. 



These secundary fibres are mixed with the root-fibres , and even 

 when the most extensive degeneration after the section of the n. 

 octavus is found , normal fibres may always be demonstrated be- 

 tween them in the distal part of the corpus trapezoides. 



As soon as the oliva superior appears , the ventral part of the 

 tegmentum, here characterised by the presence of a great number 

 of transversal fibres passing the raphe and crossing there the oppo- 

 site fibres, is no longer defined clearly towards the corpus trape- 

 /oides. But still always new fibres - now also originating from 

 the olivary nuclei - - are tending to augment these transversal fibres, 

 and in sections through the middle of the olivary nucleus, the 

 ventral part of the tegmentum so far as it is intercalated between 

 them, is totally filled up with transverse fibres. The ventral teg- 

 mental transverse fibres between the olivary nuclei never degene- 

 rate after the section of the VIII th nerve. 



In that case , however , sections touching the proximal half of 

 the olivary nuclei, demonstrate a new degeneration of root-fibres, 



