586 



fibres go to form the spinal Vth. tract, but the larger part press inta 

 the internal portion of the acusticum, where they form a distinct 

 bundle running both forward and backward. 



A part of the fibres of these nerves find their endings in the 

 acusticum. The remainder have widely separated endings. Of the 

 Vlllth. fibres, a part end in relation with the Zwischenzellen of 

 GoEONOwiTSCH (Fig. 7a). These cells I believe to be a slightly 

 specialized group of commissural cells. The remaining fibres of the 

 Vlllth., together with those of the lateral line roots and of the deep 

 portion of the Vth., take in part an ascending and in part a de- 

 scending course. All the descending fibres, except those already 

 described as the spinal Vth. and Vlllth., become arcuate fibres and 

 most, or possibly all of them, reach the opposite side (Figs. 6 — 8). 

 Their further course, I have been unable to determine. The deep 

 portion of the descending Vth. seems to go entirely to form arcuate 

 fibres. The ascending fibres have the following course. A part of 

 the Vlllth. fibres go to form a slender, compact, round bundle close 

 to the central cavity, and end in relation with certain small cells 

 which closely invest the bundle, their dendrites wrapping round and 

 piercing through it. The remainder of the Vlllth. fibres and all the 

 ascending lateral line fibres run up to the cerebellum, most of them 

 spreading out in the lateral lobes and the remainder entering the 

 body. The ascending fibres of the deep portion of the Vth. enter a 

 nucleus at the anterior end of the medulla (Fig. 9, Nuc. of med. 

 trig.) which is immediately continuous with the body of the cere- 

 bellum. 



A partially isolated portion of the tuberculum acusticum lies above 

 the cerebellar crest toward the anterior end of the medulla. This is 

 the Lobus trigemini of Goronowitsch. A large nerve root enters this 

 structure, and, as shown by Goronowitsch, this root together with 

 a root entering the acusticum immediately ventral to the cerebellar 

 crest (T. II d. and T. II v. of G.) form nerves which we know to be 

 the Ramus ophthalmicus superficialis, R. buccalis, and part of the 

 R. hyomandibularis of the Facialis, In other words, these two roots 

 constitute the lateral line Vllth. The ventral one has been described 

 above and both are shown in Fig. 7. A considerable number of fibres 

 entering the acusticum in the ventral of the two roots pass directly 

 around the inner side of the cerebellar crest and enter the so-called 

 L. trigemini. The minute structure of the L. trigemini is identical 

 with that of the acusticum, and both are directly connected anteriorly 

 with the granular layer of the cerebellum. Both also bear the same 



