OF THE NERVUS OCTAVUS. 89 



has arisen amongst the authors concerning this region , I prefer 

 giving a description of the cellular structure of the nucleus dorsalis 

 N. octavi and its surroundings , before describing the entrance of 

 root-fibres or the exit of the secundary fibres. 



In a cell-preparation from the dorsal nucleus at its greatest 

 extensity four groups of cells may be demonstrated (Plate III fig. 

 7A II ae\ 



a. a medial group (in a) 



b. a principal, dorsal (in b] or central group 



c. a lateral group (in c] 

 (I. a ventral group (in d] 



without reckoning to it a fifth group, the cells of the 



e. nucleus nervi VI , which are closely allied to , and perhaps 

 are a part of the dorsal nucleus (in e}. 



Prom these four groups, the three first named have nearly the 

 same structure. Small cells are found in them, mostly elliptical or 

 polygonal cells. Occasionally a larger pyramidal cell is found among 

 the small ones. Together they allow the description as one single 

 larger cell-mass. The principal or dorsal cell group was already present 

 at the distal end of the nucleus, and as the nucleus exfoliated two 

 alae were adjoined to it, the one medially , the other laterally, which 

 again disappeared at the capital end. But as to the fourth group, 

 it is quite another case. Its structure differs very much from the 

 other three. The reason to distinguish the three former named one 

 from another, is chiefly their relation to the auditory root-fibres. 



l ly . The medial group of cells (Plate VII fig. 7 A PI in d) 

 has nothing to do with rootfibres. Situated, in distal sections, 

 dorsally from the genu N. VII, in proximal sections, medially from 

 it, it never is found covered with black granules, neither after 

 cochlea-removal, nor after section of the nervus octavus. 



2 ly . The lateral group of cells (PJate VII fig. 7 A--H in c] 

 appears in the level of the tuberculum acusticum. It is laterally 

 bordered by the smaller cells in the deep grey layer of this nucleus 

 and medially by the cells of the principal group. But the separa- 

 tion between those cells is not very distinct. 



As we have already seen, after removal of the cochlea, the 

 degenerated root-fibres enter in its distal regions, from the outer 

 layers of the radiation of the stratum latero-dorsale. 



But as soon as the tuberculum acusticum does no longer cover 

 dorsally the C. R. and has retired laterally (Plate VII fig. 7 H in c) 

 this lateral group of cells is thrown more medially, because the portio 

 interna of the C. R. is penetrating between it and the tub. acusticum. 



