140 TEIJI HOSHINO 



(Brandis, '93 a; Winkler, '91; Wallenberg, '03). This area 

 of fiber tracts is not so well defined in regard to the separate 

 fibers as in the normal, owing to the poor development of the 

 myelin sheaths and small size of the fibers. This is one of the 

 striking differences in all affected birds from the normal. The 

 internal arcuate fibers which appear more proximally in the 

 medulla oblongata are less distinct than those of the normal; 

 this is especially easy to see at the raphe, where they decussate. 

 The thickness of the external ventral arcuate bundle, which 

 runs ventrally along the periphery of the medulla, gathering 

 fibers from the posterior and also lateral funiculus, is reduced 

 by one-third of the normal; the individual fibers are much 

 thinner in reference to the myelin sheaths and are also reduced 

 in number. This finding makes another striking difference in 

 all affected birds not only at this level, but also at other levels 

 of the medulla. 



The level of the nucleus olivaris inferior. The nucleus olivaris 

 inferior in the pigeon appears at the level of the hypoglossal 

 root and lateral to it, but it is partly pierced by this nerve in 

 the ventral region of the medulla oblongata. It lies in a trans- 

 verse position, having a thick gray mass at the lateral end. 

 Brandis only described "ein grosses fast faserfreies Feld" at this 

 level without paying any further attention to the olivary nucleus. 

 Yoshimura ('10) found experimentally that by injury to the 

 cerebellum this nucleus degenerated almost totally contra- 

 lateral^. The olivary nucleus is connected by way of the 

 arcuate fibers to the cerebellum homo- and contralaterally and 

 has a direct connection with the spinal cord. The median 

 part of this nucleus contains a rich fiber network with few cells. 

 Shimazono infers from his experimental and embryological 

 study that almost certainly fibers from the olivary nucleus 

 cross in the raphe and go dorsally to the cerebellum. 



In all our preparations except only the case of the pigeon 

 no. K207, the nucleus olivaris inferior is poorly developed; 

 the nucleus is small; the normal measures transversely 0.668 

 mm. and ventrodorsally 0.367 mm., while the affected specimens 

 measure 0.418 mm. transversely and 0.117 mm. ventrodorsally. 



