136 TEIJI HOSHINO 



fibers appear in the medulla oblongata. This nucleus is com- 

 posed of many large and small groups of cells and is supposed 

 to correspond to the nucleus dentatus of mammals (Wallen- 

 berg, '98). We may divide this into five groups, according 

 to Shimazono, though each division is not sharp, and some- 

 times it is difficult to define each part exactly, especially the cell 

 group located ventrally near the base of crus cerebelli, where 

 the arrangement of cells becomes diffuse and they pass over 

 into the cell group in the dorsal area of the acoustic field. No 

 remarkable differences of these nuclei in the affected birds 

 can be detected from the normal. 



The nucleus cerebellaris medialis which is located proximal 

 to the former nucleus shows a large round form at its maximal 

 development. This is said to correspond to the nucleus fastigii 

 of mammals and is said to give origin to the efferent cerebello- 

 spinal tract (Shimazono, '12). It measures 1.035 mm. in trans- 

 verse and 1.202 mm. in the dorsoventral diameter; the size 

 of the ganglion cells varies from 26.5 to 35.3 ix in the average 

 normal pigeon. The measurements of the same in the affected 

 birds show no changes. It is of the same size and contains 

 just as many cells. 



At the level of these cerebellar nuclei, the medullated cere- 

 bellar body appears distinctly and it has a direct connection 

 with the medulla oblongata, through the cerebellar peduncle. 

 The lateral portion of the cerebellar body, notwithstanding the 

 normal size of the cerebellar nuclei as already stated, is reduced 

 in area both in reference to fibers and gray substance. The 

 myelinated fiber mass just lateral to the nuclei measures 0.418 

 to 0.585 mm. on the average in the affected birds, while in the 

 normal it measures 0.668 to 0.752 mm. Individual fibers stain 

 a more or less light blue color in the affected birds, while in the 

 normal they stain a deep purple-black; the myelin sheaths 

 themselves are also thinner. This is true in all the affected 

 specimens. Nevertheless, no positive proof of degeneration of 

 the processes can be made out. 



The molecular layer at this ventrolateral part of the vermis 

 is reduced in breadth in all affected birds sometimes one-half 



