Johnston, The Brain of Petroniyzon. 31 



There is a central fiber mass in the right ganghon surrounded 

 both internally and externally by a thick zone of cells. On 

 the left side there is a slight internal collection of cells, but 

 throughout most of the ganglion cells and fibers are mingled. 



The cells in both ganglia closely resemble those in the 

 same ganglia in Acipenser (Fig. 16). They are pyramidal, uni- 

 polar cells which give off the neurite from some part of the 

 dendrite. The neurites collect in the caudo-lateral angle of each 

 ganglion to form the bundle of Meynert. The right bundle 

 is very much larger than the left and contains both fine and 

 medium fibers. In general the coarser fibers arise from the 

 cells of the ganglion while the fine fibers end by short branches 

 in all parts of the right ganglion. Some of the coarser fibers 

 end in the ganglion, however, and a ftw fine ones arise there. 

 The bundles take the usual course through the walls of the 

 mid brain, the large right bundle lying closer to the cavity than 

 the left, but not causing a ridge on the internal surface as in 

 the species described by Ahlbokn. Both bundles are very far 

 removed from the cavity in the lower part of their course (Fig. 

 16). The bundles arrive at the ventral surface of the mid 

 brain just behind the corpus mammillare and, making a turn 

 mesad at nearly right angles, begin to decussate. At tiie same 

 time a large bundle of fine fibers constituting nearly one third 

 of the right bundle leaves the ectal surface of that bundle and 

 continues caudally (Fig. 16). A few fine fibers continue cau- 

 dally from the left bundle and become arranged in a definite 

 fasciculus farther caudad. The details of the decussation are 

 difficult to make out owing to the fact that in all my Golgi 

 preparations nearly all the fibers are impregnated. Sufficient 

 can be made out, however, to show that the main features of 

 the decussation and the place of ending are the same as in Aci- 

 penser. There is a large nucleus in the same position as the 

 end nucleus in Acipenser, extending caudally from the decus- 

 sation of the III nerve at either side of the ventral groove of 

 the ventricle to the level of VIII. At the level of III there is 

 a considerable collection of cells between the decussation of 

 III and that of Meynert's bundles which probably belong to 



