MEDULLA OBLONGATA IGl 



Triturus also (Larsell, '31, p. 50) and is comparable with the second- 

 ary vestibulo-cerebellar tract of mammals. Fibers descending from 

 the auricle into tracts a and b are probably ancestral to the mam- 

 malian f. uncinatus of Russell. 



At the bulbo-spinal junction, tract b merges with the spinal root 

 of the vestibular nerve, and its fibers descend for an undetermined 

 distance in the lateral fascicles of the dorsal funiculus of the cord. 

 There is, accordingly, a dorsal vestibulo-spinal connection by both 

 peripheral and secondary fibers, a connection which puts the vestibu- 

 lar apparatus into especially intimate relation with the neuropil of 

 the nucleus funiculi. It is probable that fibers ascend from the nucleus 

 funiculi in tract b, and some of these may extend as far as the auricle. 

 As I have pointed out ('44&), this cerebellar connection, if confirmed, 

 would be the obvious precursor of the system of arcuate cerebellar 

 fibers described in primates by Ferraro and Barrera ('35) as passing 

 from the external cuneate nucleus to the cerebellum by way of the 

 corpus restiforme. Tract b connects only with the vestibular field of 

 the cerebellum, and this cerebellar connection of the nucleus funiculi 

 (if present) would have a physiological significance quite different 

 from that of the larger connection by way of the tractus spino- 

 cerebellaris (fig. 3), for the latter connects only with the non vestibu- 

 lar body of the cerebellum. 



In addition to the dorsal uncrossed vestibulo-spinal connection 

 just described, there is an extensive crossed and uncrossed connection 

 between tract b and the motor field by arcuate fibers. Many of these 

 fibers bifurcate, with branches which ascend and descend in the 

 ventral funiculus. These may correspond with the secondary vestibu- 

 lar fibers of the mammalian f. longitudinalis medialis, but here they 

 are dispersed, and the details of their courses have not been de- 

 scribed. In the absence of elective impregnations, our material does 

 not reveal their courses. Their presence may be expected, in view of 

 the fact that they comprise an important constituent of this fascicu- 

 lus in mammals. An incomplete impregnation in an advanced larva 

 gives some evidence of them. In figure 38 the contorted fiber directed 

 medially from the region of entrance of the VIII root is probably a 

 secondary vestibular fiber, which enters the f . longitudinalis medialis, 

 and the two impregnated fibers seen in this fasciculus may belong to 

 this system. 



The inferior olive has not been identified in urodeles, but among 

 the dispersed arcuate fibers are some with connections which suggest 



