BRAINS AND SPINAL CORDS IN ATAXIC PIGEONS 143 



base of cerebellar peduncle, the size of each cell, however, is 

 not changed; the large cells in this area are 39.9 /x in diameter 

 in both the normal and affected. These reductions of two 

 nuclei, nevertheless, are by no means striking. The so-called 

 'Bogenzug' of Brandis or the dorsal fiber system of the n. octavus 

 in the acoustic area runs from or around the nucleus parvo- 

 cellularis partly to the raphe and partly dorsally to the cere- 

 bellum. Both fiber paths of this bundle are sometimes slightly 

 thinner in the affected cases, though there is no striking varia- 

 tion from the normal. The fibers that are around or come from 

 the nucleus magno-cellularis and that run dorsally to form 

 the medial part of the cerebellar peduncle and that then pass 

 across the peduncle obliquely to enter the cerebellar cortex 

 exhibit no differences from the normal. 



A fiber bundle which runs dorsomedially to ventrolateral^, 

 from the ventrolateral border of the nucleus parvo-cellularis 

 to the small round nucleus medial to the spinal root of the n. 

 V. appears plainly at the more proximal level, where the sensory 

 nucleus of the trigeminal nerve appears. This fiber bundle 

 and nucleus appear quite the same in both the affected and 

 healthy birds. They seem to correspond to the beginning 

 portion of the ventral system of the central acoustic nerve, 

 as was brought out by Wallenberg ('98). The further cerebral- 

 ward course of fibers from this nucleus which cross the abducens 

 root at its ventral two-thirds is not easily differentiated 

 from internal arcuate fibers in any of our normal or ataxic 

 preparations. 



The restiform body at this level is much more apparently 

 reduced; its size is often one-half the normal, on the average 

 the transverse diameter is 0.200 to 0.251 mm. in the affected, 

 and 0.334 to 0.418 mm. in the normal. The fiber mass cross- 

 sectioned just medioventral to the restiform body is not as large 

 as in the normal section. The cerebellar peduncle appears at 

 this level connecting the cerebellum and medulla oblongata 

 in frontal section. The peduncle is markedly reduced in its 

 whole transverse breadth; 1.336 mm. in the affected and 1.754 

 mm. in the normal. This reduction is due to the thinness of 



