630 'Journal of Comparative Neurology and Psychology. 



jiinctivum whose fibers are lightly medullated. In Fig. 24 the 

 greater part of the fibers have turned ventrad and are cut across in 

 the section. Owing to the fact that the fibers of this bundle are cut 

 across in the frontal series, their course will not appeal so quickly 

 to the eye in the following figures as in those taken from the trans- 

 verse series, but the evidence of the relations of the fibers will be 

 much more complete from an examination of both series of figures. 

 In Fig. 24 the mesencephalic root appears as several small bundles 

 of fibers obliquely placed in the section. The fibers may now be 

 grouped into three main areas as an aid in tracing their further 

 course. These areas are indicated roughly by the position of the 





Fig. 25. The third section of this series ventral to the last. X 20. Descrip- 

 tion in text. 



letters a, h and c. The fibers adjacent to h and c form one fairly 

 continuous flattened bundle which is wider cephalo-caudad. Adjacent 

 to a are numerous oblique fibers, some of which are longer than 

 others. These belong to the more ventrally placed bundles in the 

 mesencephalon and are just now joining the root-bundle. Between 

 a and the bundle h-c in this figure are some intermediate fibers whicli 

 in Fig. 25 have joined h or c. In Fig. 26 the motor nucleus appears 

 and is outlined by a dotted line and by the motor bundles which 

 partly embrace its caudal surface. At least a part of the broad 

 bundle running diagonally past the motor nucleus consists of decus- 

 sating motor fibers from the other side. For convenience the motor 

 bundles will be designated by the last letters of the alphabet and 

 these decussating fibers are labeled z, while the homolateral bundles 



