Kingsbury, Bj-ain of Nectunis. 1.7 1 



metacoele causing, apparently, a slight bulge of the floor. In 

 the region of the eighth nerve the relations are more compli- 

 cated : the root of the seventh passes laterad to its exit, and 

 the decussation of the Mauthner fibers occurs. In connection 

 with the latter are associated many fibers of this bundle, and 

 other finer fibers from more ventral regions. Other coarse 

 fibers appear to pass laterad without crossing the meson. Ceph- 

 alad of the seventh and eighth nerves, the size of the bundles 

 is much reduced owing to the loss of fibers. They, with the 

 other longitudinal myelinic tracts, gradually become separated 

 from each other, an amyelinic area intervening (Fig. 20). Oc- 

 casional decussations still occur, however, the last just caudad 

 of the fifth, where the large fiber could be traced to the imme- 

 diate neighbood of a large isolated cell, in the extreme lateral 

 region of the oblongata. Although actual continuity was not 

 demonstrated, it is probable from the results attained in other 

 forms that many of the fibers which end near the level of the 

 eighth nerve spring from the cells of the ventral region, which, 

 as Osborn found in CryptobrancJius, are particularly large and 

 numerous in that immediate neighborhood. Likewise the ori- 

 gin of the decussating fibers from the large, laterally situated 

 cells near the exit of the auditory nerve, may be tentatively 

 held. 



Some of the fibers in the ventral columns pass dorsad into 

 the cinerea in the region of the tenth (X^) and ninth nerves, in 

 close relation to the nidus of the seventh and the fibers of that 

 nerve. The relations of these fibers were much clearer in 

 Aviblystoma than in Necturus, due to their closer association into 

 a bundle in that form. Similarly, more laterally situated fibers 

 with thick myelinic sheaths terminated in the cinerea near the 

 exit of the eighth nerve. A comparison of these with the lat- 

 eral uncrossed Miillerian fibers of Petroniyzon, as Koppen ('88) 

 has done for similarly situated fibers in the frog, is attractive. 

 In addition to the above, other coarse fibers gradually migrate 

 dorsad and laterad to lie directly ventrad of the cinerea, and ter- 

 minate, a lateral group in the region of the motor nidus of the 



