152 TEIJI HOSHINO 



nucleus of the trigeminal nerve as a fiber mass running from the 

 ventral part of the cerebellar peduncle to the medial part of the 

 medulla. This brachium is perfectly normal in the affected 

 specimens. The decussation of the brachium as well as the nu- 

 cleus ruber at the proximal region of the oculomotor nerve are 

 well developed. 



As to the connection of the cerebellum to the fasciculus longi- 

 tudinalis medialis, no definite structure could be identified. 



The levels of the trochlear and oculomotor nuclei. The troch'ear 

 nucleus, its size, shape, and number of cells, together with the 

 fibers coming from the nucleus in the affected specimens, all ap- 

 pear as in the normal sections. The whole dorsoventral diameter 

 of the brain stem at this level of the nucleus trochlearis measures 

 in the midine 3.507 mm. in the normal and 2.922 mm. in the af- 

 fected section. The entire width of the brain stem from side to 

 side measures 5.511 mm. in the normal and 4.843 mm. in the 

 affected. These measurements show a reduction of the brain 

 stem at this level, but the small size is chiefly due to a diminu- 

 tion in area of the reticular formation. The ventral arcuate 

 bundle has already disappeared. 



The oculomotor nucleus appears proximal to the trochlear 

 nucleus as its continuation, medial and slightly dorsal to the f asc. 

 long. med. The dorsolateral centers of this nucleus contain small 

 well-defined cells, but the other centers have large cells. From 

 the nucleus fibers emerge passing ventrally, part of them crossing 

 the raphe, where they form the internal fibers of the opposite 

 oculomot or nerve. At the point of emergence of the nerve fibers 

 from the brain stem, there appears in the nerve stem a half- 

 moon-shaped, colorless line in the Weigert preparation. This 

 condition may be a structure analogous to that already discussed 

 in the cranial nerve roots in the human by Thomsen ('87), Hulles 

 ('06) and Staderini ('90). No pathological or defective devel- 

 opment in the oculomotor nerve fibers or in its nucleus is visible 

 in the affected pigeons. 



The fasc. long. med. in this region is small and appears less oval 

 than the normal, but the reduction is not as marked as at the 

 former levels; it measures transversely 0.317 mm. in the affected, 



