142 TEIJI HOSHINO 



The zone of fibrae arcuatae externae ventrales is extremely 

 thin and contains only a few fibers and stains less intensely 

 than normal. The area of the fasciculus long. med. and pre- 

 dorsalis shows diminished transverse as well as ventrodorsal 

 dimension, especially the former. In the distal portion of the 

 medulla oblongata, this fasciculus long. med. cannot be sepa- 

 rates from the fiber tract which lies ventrally to this fasciculus. 

 The area of this fasciculus contains many smaller fibers, all 

 more variable in size than the normal; the average caliber is 

 5.7 ju in the ataxic and 8.6 ix in the normal; the staining also 

 not so deep as in the normal. Nucleus of the ala cinerea and 

 the fibers of the vagoglossopharyngeus are normal. 



All above findings are quite uniform in all affected pigeons, 

 there being only a difference in degree. 



The level of the cochlear nuclei. The acoustic nerve enters 

 the medulla oblongata in two roots as in mammals; the one is 

 the dorsal, distal, or lateral root, the nervus cochlearis; the 

 other is the ventral, proximal, or medial root, the nervus vestib- 

 ularis. The nuclei of the acoustic nerve are divided into 

 three main groups: One, the nucleus angularis, 'Eckkern,' 

 located at the dorsolateral portion of the medulla, into which 

 the cochlear root enters; this corresponds to the tuberculum 

 acusticum of mammals (Brandis, '94; Winkler, '91). The 

 second nucleus appears in the lateral wall of the fourth ventricle, 

 crescent-shaped, surrounded by a medullated fiber mass, and is 

 named the nucleus parvo-cellularis, 'der kleinzellige Kern.' 

 The third one, the largest, occupies the space between the above 

 two nuclei, nucleus magno-cellularis, 'der grosszellige Kern.' 

 The magno-cellular nucleus is supposed to be analogous to the 

 nucleus Deiters in mammals. 



The nucleus angularis as well as the cochlear stem in all four 

 ataxic birds are almost the same in the normal in reference 

 to their developmental conditions. The nucleus parvo-cellu- 

 laris has sometimes a little narrower shape and the medullated 

 fibers around it appear to be slightly reduced. The nucleus 

 magno-cellularis, though it appears almost the same as normal, 

 seems to be diminished at its proximal dorsal portion in the 



