BRAINS AND SPINAL CORDS IN ATAXIC PIGEONS 145 



to the raphe, where it enters into the fasc. long. med. Some of 

 the fibers of the first group disappear into the fiber group sur- 

 rounding the nucleus parvo-cellularis, giving apparently fibers to 

 this nucleus, while others run dorsally and laterally and enter 

 into the cerebellar peduncle. The second group of the vestibular 

 fibers runs transversely, as already seen, toward the raphe, be- 

 neath the nucleus parvo-cellularis and the so-called 'Bogenzug' 

 of Brandis, to enter the raphe. 



The breadth of the stem of the n. vestibularis just outside of 

 the medulla oblongata in all affected birds has the normal dimen- 

 sion, both being 0.585 mm. The nucleus of this stem which is 

 analogous to the ganglion of Scarpa in mammals shows no dif- 

 ference from the normal. At the lateral portion of the medulla, 

 after passing through the restiform body, the intrabulbar vestib- 

 ular fiber bundle increases in its dimension; it measures on the 

 average 0.835 mm. in the affected as well as in the normal birds. 



When we pursue the vestibular fibers transversely from the 

 periphery toward the raphe, however, we find differences in the 

 floor of the fourth ventricle at the place where the vestibular fibers 

 meet the fasciculus long. med. In the ataxic, the bundle of fibers 

 which goes from a connection with the vestibular nerve fibers 

 and the 'Bogenzug' just at the lateral side of the fasc. long, med., 

 where they leave this fasciculus, is markedly reduced in dimension, 

 being about two-thirds that of the normal. Both of the fasciculi 

 long. med. in their transverse diameter measure 0.835 mm., while 

 in the normal they measure 1 .086 mm. on the average. In pigeon 

 no. K137 the transverse diameter is only 0.718 mm. The ven- 

 trodorsal diameter of the fasc. long. med. including fasc. predor- 

 salis, on the contrary, is not very much reduced, 1.002 mm. in 

 the normal and 0.919 mm. in the ataxic; often both measure the 

 same. In the area of the fasc. long, med., the fiber bundle along 

 the raphe, running ventrodorsally, is reduced in its transverse 

 diameter; in the affected pigeon it measures 0.08 mm., while in 

 the normal it measures 0.167 mm. The fibers crossing trans- 

 versely in the triangular area of this fasciculus are also apparently 

 diminished in number. The longitudinal fibers are diminished 

 and the average caliber of each fiber is 5.7 y. in the affected and 



