362 C. JUDSON HERRICK 



commissure and IV nerve. IVIention was also made of a coarse 

 fibered tract seen by Osborn ('88) and Kingsbury ('95) which 

 appears to accompany the mesencephahc V fibers and can be 

 followed caudad as far as the roots of the VII and VIII nerves. 

 Norris ('13, p. 269) describes these fibers in Siren as a portion of 

 the more posterior of the two rootlets by which the mesencephalic 

 V fibers enter the brain, this posterior rootlet dividing into ante- 

 riorly and posteriorly directed tracts. The latter tract passes 

 backward at the ventral border of the gray matter ''and can be 

 traced as far posteriorly as the level of the root of the seventh 

 nerve." 



This description of Norris I confirm, and add the further obser- 

 vation that in Amblystoma not only do the bundles of root fibers 

 of both the anterior and posterior rootlets divide into ascending 

 and descending tracts, but the individual fibers of the mesen- 

 cephalic V root bifurcate to enter these tracts. This can 

 be very clearly seen in several of my specimens in horizontal 

 Cajal preparations. Figure 54 illustrates such a horizontal sec- 

 tion taken at the level of the bifurcation of several of the mesen- 

 cephalic V root fibers. These root fibers are coarser than any 

 others in the preparation and can readily be separately followed 

 for their entire length throughout the series of sections. The 

 section figured is tangential to the ventral border of the stratum 

 griseum and the adjacent section dorsalward includes neurones of 

 the motor V and motor VII nuclei at the locations designated, 



Some of our preparations show slender collateral branches of 

 the mesencephalic V root fibers entering the motor V nucleus, but 

 these are not visible in the preparation figured. The descending 

 branches are, however, clearly shown, these branches being in 

 many cases as large as the stem fibers from which they arise. 

 They pass backward and inward and arborize among the dendrites 

 of the motor VTI neurones. The ascending branches of these 

 root fibers can readily be followed to the tectum mesencephali, as 

 in Necturus, few of these fibers crossing in the decussatio veli. 

 In the tectum these very coarse fibers form the deepest elements 

 of the stratum album, from which they turn abruptly inward one 

 at a time to enter their respective cell bodies of the nucleus magno- 



