144 TEIJI HOSHINO 



the spinocerebellar tract and bundles from the arcuate fibers 

 which form the main portion of the restiform body, and is 

 observed in all serial sections in all the affected birds. 



The fiber bundle along the ventral periphery of the medulla 

 is quite thin in all affected pigeons. This is indeed very striking; 

 the ventrodorsal thickness of this bundle measures 0.100 mm. 

 in the normal and 0.043 mm. in the affected bird — a dimension 

 of less than one-half the normal. There is not only a reduc- 

 tion of thickness of the bundle, but each individual fiber is 

 smaller and stains weakly owing to its thin myelin sheaths. 

 The above condition of this bundle throughout its course is 

 common in all affected birds and it constitutes one of the most 

 decided changes in the medulla. 



The internal arcuate fibers are less prominent and quite indis- 

 tinct, owing to the reduction in fibers, their poor staining proper- 

 ties and the small size of the individual fibers; the scattered large 

 ganglion cells between the fibers in the reticular formation are 

 not only few in number, but also small in size, the average size 

 of the large cells being 22 . 8 to 37.5 /x in the affected and 28.5 to 

 57.0 ix in the normal. The area of the reticular formation is 

 apparently reduced. 



The tall triangular area of the longitudinal fiber bundle along 

 the raphe with its base directed dorsally to the floor of the fourth 

 ventricle, that is, the area of the fasc. long. med. and predorsalis is 

 smaller, especially in its transverse diameter, this measuring 0.638 

 mm. in the affected and 0.985 mm. in the normal. The fibers 

 which cross the raphe from side to side and the fibers which run 

 ventrodorsally in the raphe in this area are quite scant. The 

 fibers, both the longitudinal and transversal, are thin, indistinct, 

 and do not stain a deep black by Weigert. The spinal root of 

 the trigeminal nerve shows a good development in both the 

 healthy and unhealthy birds. 



The level of the vestibular nerve. Proximal and a little ventral 

 to the cochlear stem, the nervus vestibularis appears as a large 

 bundle entering the medulla oblongata. A part of the fibers 

 runs dorsally to the acoustic area, to the nucleus magno-cellu- 

 laris, while the other and greater part of the fibers runs medially 



