^6» THE liRAIX OF THE TIGER SALAMANDER 



sections see '"io, ^gs. -2-7. and 'il , figs. '■28-oo, tr.hab.pcd.). As it enters 

 the peduncle, it turns outward, passing ventrolaterally thriiugh tlie 

 alba to reach the surface near the superficial origin of the III nerve 

 root. Passing ventrally of these emerging root fibers, it turns medially 

 at the fovea isthmi, immediately spinahvard of which it enters its 

 decussation in the ventral commissure (figs. 50, 51, 53). The spiral 

 endings of these fibers are described in chapter xiv. In the alba of the 

 peduncle it passes internally of the area ventrolateralis pedunculi and 

 well separated from this superficial neuropil {fig. 94). Here many 

 thin axons separate from the fasciculus to enter the superficial neu- 

 ropil. A little farther spinalward. at the level of the III nerve root, a 

 larger number of fine fibers leave the fasciculus and turn forwartl into 

 the posterior end of the neuropil, as shown in a favorable (lolgi sec- 

 tion ('4^, fig. 40, fibers from, f.retr. to a.I.t.). 



This is the usual arrangement. That the connection of the f. retro- 

 flexus with the area ventrolateralis pedunculi is important physio- 

 logically is evident from atypical courses of the fasciculus which have 

 been observed in a number of specimens, always on one side only. 

 One such anomaly is well illustrated in figures 56. 57. and 58. In this 

 specimen (horizontal Golgi sections) the right f. retroflexus is un- 

 stained but can be seen to take the usual course; the left is abundant- 

 ly impregnated from the habenula to its decussation. As it enters the 

 alba of the peduncle it divides into two bundles. The medial bundle, 

 containing about one-third of the fibers, takes the typical course: the 

 larger lateral bundle passes along the inner border of the area ventro- 

 lateralis pedunculi with numberless terminals or collaterals entering 

 this neuropil and spreading in the surrounding alba. Both bundles 

 pass spinalward under the emerging III root fibers and converge to 

 the decussation below the fovea isthmi. Many of these fibers spread 

 in the alba rostrally and caudally of the fovea without decussation. 



Another adult specimen (^no. "2'-217) from the same. lot and similarly 

 prepared is like that just described except that the lateral bundle is 

 smaller than the medial. This smaller bundle enters the area ventro- 

 lateralis and here breaks up into several slender fasciculi. Posteriorly 

 of this area of neuropil, these fasciculi, somewhat diminished in vol- 

 ume, i-ejoin the medial bundle at the level of the III nerve root and 

 both bundles then enter the decussation. This arrangement is found. 

 on one side only, in the series of sagittal Golgi sections from which 

 figures 7'2 and 73 were drawn. A somewhat different atypical feature 



