MEDULLA OBLONGATA OF AMBLYSTOMA 375 



From the lower end of the oblongata to the V roots these fibers 

 are all assembled into a compact fascicle ventrally of the spinal V 

 root (figs. 9 to 17). Golgi sections show terminals from this 

 tract turning inward to end throughout the motor tegmentum as 

 far forward as the eminentia subcerebellaris tegmenti and especi- 

 ally among the dendrites of the motor VII and motor V nuclei. 

 This is the tractus spino-bulbaris. In the vicinity of the V roots, 

 in both the larva and the adult, special fascicles leave this tract to 

 terminate in the chief sensor}^ V nucleus under the eminentia 

 trigemini, some of these fascicles ascending in company with the 

 ascending sensory V root fibers far forward under the cerebellum. 

 These fibers constitute a tractus spino-bulbaris trigemini (figs. 

 7, 8, tr.sp.b.), and probably serve to bring spinal cutaneous 

 nervous impulses forward into relation with those from the skin of 

 the head in the eminentia trigemini. 



Shortly below the level of the V roots the mixed tract divides 

 into a lateral spinal lemniscus portion (figs. 10, tr.sp.t.) and a 

 more medial spino-C(irebellar portion (tr.sp.cb.). Under the body 

 of the cerebellum the latter portion (figs. 7, tr.sp.cb.) turns abruptly 

 dorsalward and divides into two parts. Some of these fiber;^ end 

 in the body of the cerebellum of the same side and a larger 

 number of them continue directly upward to enter the conmiissura 

 cerebelli and finally to terminate in the cerebellum of the opposite 

 side. 



In my examination of the cerebellum of Necturus ('14, p. 7) 

 I described, in addition to the tract just described, a tractus 

 spino-cerebellaris dorsalis. More complete study of these tracts 

 has not yielded a clear separation of the latter tract, the fibers so 

 described, if present at all, being so mingled with other systems as 

 to make their separate identification uncertain. In the aberrant 

 teleost, Mormyrus, Stendell ('14) has recently described a spino- 

 or bulbo-cerebellar tract which arises at the caudal end of the 

 oblongata from the terminal nucleus of the fasciculus dorso-lateralis 

 of the spinal cord. This large tract passes for its entire length 

 through the oblongata dorsally of the spinal V root, and may be 

 the equivalent of the tractus spino-cerebellaris dorsahs which I 

 provisionally identified in Necturus. 



THE JOURNAL OP COMPARATIVE NEUROLOGY, VOL. 24, NO. 4 



