148 TEIJI HOSHTNO 



parently diminished in number. This nucleus appears in frontal 

 section, and proximally disappears at the level where the troch- 

 lear nucleus shows its largest size. In the affected preparation, 

 on the other hand, the nucleus disappears at the level just prox- 

 imal to the place of appearance of the sensory nucleus of the 

 trigeminal nerve. 



This nucleus has never been exactly described, even though it 

 seems to be similar to the oliva in Friedlander's illustration ('98) 

 or the medial « -nucleus ('Trapezkern,' Westphal) of Wallenberg 

 ('04) in reference to its localization. The inferior olivary nucleus 

 of the pigeon lies, however, far distal and lateral to the hypo- 

 glossal root, while the superior olivary nucleus lies more dorsal- 

 ward, as already described. If this nucleus had a connection 

 with the fiber bundle of the ventral system of the eighth nerve, 

 like the superior olivary nucleus and the nucleus isthmi, it would 

 be normal as these are. Thomas ('11) reports the atrophy of the 

 arciform nucleus in cerebellar atrophy, and contends from his 

 experiments that the arciform nucleus has close relation with the 

 pontine nucleus. It seems to me rather, therefore, that this 

 nucleus may have some close physiological relation to the already 

 described ventral fiber bundle or to the arcuate fibers than to 

 the ventral system of the eighth nerve. 



The internal arcuate fibers in the reticular formation are fewer 

 and paler; differences especially marked in the fibers which cross 

 at the raphe. At the lateral edge of the brain stem, a fiber mass 

 runs toward the cerebellum passing through the cerebellar pe- 

 duncle, which measures 0.25 mm. in the normal and 0.08 mm. in 

 the affected birds. Going more proximally from this level, the 

 fasc. long. med. becomes more and more round in section and the 

 cerebellar peduncle decreases in breadth. 



At this point it will be well to describe more thoroughly the 

 cerebellar peduncle, from its distal to proximal end, for reduction 

 of this peduncle is one of important differences in the affected 

 birds. 



The distal connection of the medulla oblongata to the cere- 

 bellum in frontal sections begins at the level of appearance of 

 the cochlear nerve. The spinocerebellar tract at the lateral 



