BRAINS AND SPINAL CORDS IN ATAXIC PIGEONS 141 



The number of contained cells is reduced, forty in each section 

 on the average in the normal, twenty-five on the average in 

 the affected; the size of the cells is below normal, the normal 

 cells measuring 19.9 to 22.8 ^ in diameter, but the Nissl bodies 

 show no difference from the normal. The interolivary fiber 

 bundle is markedly reduced; in the affected pigeon no. K158, 

 its ventrodorsal thickness measures 0.0835 mm. instead of 

 0.2505 mm. as in the normal. This fiber bundle, therefore, 

 is one-third the normal thickness. In other affected birds this 

 reduction is also seen, but not so markedly. In the normal 

 specimen the fibers surrounding the olivary nucleus, the cir- 

 cumolivary fibers, especially those dorsal and lateral to it, are 

 thick and well developed. We see also a fiber bundle which 

 runs from the olivary body or from its surroundings, dorsally 

 and laterally to the spinal root of the trigeminal nerve. 

 Further proximally this bundle appears at the medial part 

 of the tractus spinocerebellaris and enters the cerebellum with 

 it. This fiber mass appears less definite and stains lighter than 

 the normal deep color, so that the distinctness of the boundary 

 of the gray matter of the olivary nucleus seems to be less defined 

 in the affected Weigert preparation than in the normal sec- 

 tions. This is due to the scantiness of fibers and thin myelin 

 sheaths around the nucleus. The fibers which are seen within 

 the nucleus are also diminished in number. 



The internal arcuate fibers are few in number and do not 

 stain as deeply as the normal, and the scattered ganglion cells 

 in the reticular formation are small and not nearly as numerous 

 as in the healthy birds. The restiform body is markedly re- 

 duced, 0.200 to 0.251 mm. in the affected and 0.367 to 0.418 mm. 

 in the normal. The fiber mass which runs longitudinally at the 

 ventromedial region of the restiform body is not stained as well 

 as in the normal and contains fewer fibers. No difference is 

 recognizable in the spinal roots of the trigeminal nerve in either 

 its staining qualities or its dimensions. Fibers of the hypo- 

 glossus and the cells in the nucleus n. hypoglossi have all a 

 normal structure. 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 31, NO. 2 



