Johnston, TJic Brain of Petroinyzon. 19 



acusticum may be described best by beginning with VIII (Figs. 

 I, II, 1 1 a, 12, 29, 30). In transverse sections the VII-VIII 

 root complex is the most conspicuous of the nerve roots. The 

 VIII enters by two roots so close together that they may be 

 treated as one, somewhat ventral and caudal to the lateral line 

 VII. The VIII fibers enter the lateral acusticum nucleus and 

 a part of them end, with or without branching, in connection 

 with the spindle cells in various parts of the lateral nucleus as 

 described above. All of the remainder apparently undergo 

 bifurcation, the branches passing forward and backward. They 

 are best traced in longitudinal sections. The caudally directed 

 fibers run to the caudal end of the acusticum and some of them 

 pass beyond the level at which the acusticum is difterentiated 

 and enter the nucleus funiculi. Such fibers as do this may be 

 considered as homologous with the spinal VIII tract of Aci- 

 penser and of higher vertebrates. The fibers which pass for- 

 ward run chiefly in or over the surface of the dorso-median nu- 

 cleus and a very large part of them enter the cerebellum, where 

 they end in the granular layer. 



In sagittal sections through the lateral wall of the medulla 

 the lateral line X root is seen passing upward and forward 

 through the caudal bundles of VIII fibers (Fig. 30). The fibers 

 of this root all enter the dorso-median nucleus and, I think, end 

 in it without running forward or backward as far as the VIII 

 fibers. No bifurcating fibers have been found either in this or 

 in the lateral line VII root. 



The lateral line VII (Figs, i, ii, 1 1 a, 12, 29, 30) has two 

 distinct roots of medium coarse and very coarse fibers, one 

 cephalo-dorsal to the other. The ventral root runs close over 

 the dorso-cephalic surface of VIII. Its fibers end in part among 

 the ordinary cells of the lateral nucleus, but most of them pass 

 into the dorso-median nucleus, while a few small bundles enter 

 the lobus lineae lateralis (Fig. 1 1 a). A considerable number 

 of these fibers pass forward through the outer part of the me- 

 dian nucleus and enter the cerebellum. I have not found any 

 of these fibers turning backward. 



The dorsal root is directed much more dor.sally as it enters 



