286 THE BRAIN OF THE TIGER SALAMANDER 



Fascicles {10). — These comprise the greater part of the ventral 

 fascicles of the lateral forebrain bundles (figs. 26-32, 101, 102, 

 f.lat.t.v. and (10)). In 1927 (p. 287) this was termed tr. strio-peduncu- 

 laris, but it now appears that these fibers arborize not only in the 

 peduncle but also throughout the length of the isthmic tegmentum, 

 though they do not extend as far spinalward as those of group (9). 

 This tr. strio-peduncularis et tegmentalis arises from the ventral 

 nucleus of the corpus striatum, decussates partially in the anterior 

 commissure, traverses the ventral thalamus, and in the peduncle 

 breaks up into a number of small fascicles which are widely distrib- 

 uted among the ventral and dorsal tegmental fascicles. Its fibers are 

 less myelinated than those of group (9), and, in general, they dis- 

 tribute in the alba more ventrally and laterally (figs. 92, 102, 103; 

 '36, pp. 304, 336, fig. 6; '396, fig. 79; '42, figs. 2, 17); compare the 

 preceding description of the lateral forebrain bundles. 



Most of the numbered groups of fascicles which have just been 

 listed lie in the deeper layers of the alba close to the gray. Super- 

 ficially of these and in part mingled with them are many dispersed 

 fibers, loosely fasciculated in variable arrangements. These include 

 many of the shorter tracts mentioned in the descriptions of the sev- 

 eral regions, such as thalamo-tegmental, pedunculo-tegmental, tecto- 

 tegmental, and tegmento-bulbar tracts. The well-defined tr. olfacto- 

 peduncularis also belongs in this series. The thalamo-tegmental fibers 

 are very numerous, and some of them are well fasciculated. From 

 both dorsal and ventral thalamus uncrossed fibers stream backward 

 to the isthmus, some deeply and some superficially — tr. thalamo- 

 tegmentalis rectus (figs. 15, 31-34, tr.th.teg.r.). These are in addition 

 to the thick fibers from the ventral thalamus, which enter tegmental 

 fascicles (6) and (8), some uncrossed and some decussating in the 

 postoptic commissure (fig. 17, tr.th.teg.v.r. and c. '3.96, p. 546). Analy- 

 sis of the fibers from the dorsal thalamus which decussate in this 

 commissure is very difficult. The earlier accounts are confused and 

 inaccurate, but the essential features are now clear, as described in 

 the next chapter. 



FASCICULUS TEGMENTALIS PROFUNDUS 



This name has been given to a loosely arranged sheet of fibers 

 which borders the gray in the tegmental region of the midbrain and 

 the isthmus. Most of these fibers are unmyelinated and are part of an 



