224 THE BRAIN OF THE TIGER SALAMANDER 



fibers are joined by similar thick fibers from the pretectal nucleus 

 and dorsal thalamus (tr.fh.p.c. of the figures). 



Superficially of the connection just described, there is a large col- 

 lection of uncrossed fibers passing between the pretectal nucleus 

 (pars intercalaris diencephali) and the peduncle. These were de- 

 scribed in Necturus ('17, p. 264; '336, p. 110 and fig. 57) under the 

 name "tr. thalamo-peduncularis dorsalis superficialis." These fibers 

 are spread close to the pial surface in the wide di-mesencephalic fis- 

 sure and end in large numbei-s in the neuropil of the area ventro- 

 lateralis pedunculi. Some of them also reach the hypothalamus. The 

 condition in Amblystoma is similar, thus bringing the pretectal 

 nucleus into intimate relation with terminals of the basal optic tract 

 and the oculomotor nucleus. 



3. Tr actus tecto-thalamicus et hypothalamicus cruciatus (fig. 12, 

 tr.t.th.h.c.a. and p.\ see also the section on com. postoptica in chapter 

 xxi). — The anterior and posterior divisions of this complex were 

 described in 1942 (p. 221). The anterior tract passes from the dorsal 

 part of the superior colliculus to the hypothalamus, decussating in 

 the postoptic commissure. It is here termed "tr. tecto-hypothalami- 

 cus anterior" (figs. 25-36, tr.t.hy.a.; see further on p. 296). It has 

 connections with the thalanms and hypothalamus of both sides, and 

 some of its crossed fibers may reach the peduncle and tegmentum. 



The posterior division arises chiefly from the inferior colliculus, 

 with accessions from the ventral border of the superior colliculus. 

 It lies parallel with the anterior division and, more posteriorly, par- 

 tially decussates in the postoptic commissure and has terminals in 

 the thalamus and hypothalamus of both sides (figs. 25-35, 

 tr.t.th.h.c.p.). Its thicker and more myelinated fibers continue as tr. 

 tecto-tegmentalis cruciatus into tegmental fascicles of groups (6) and 

 (8), to end in the peduncle and tegmentum as far back as the VII 

 nerve roots. The distribution of these fibers suggests that they are 

 primarily concerned with mass movements and local reflexes of the 

 musculature of the head and probably also with conditioning of these 

 movements. What seems to be the equivalent of this tract is de- 

 scribed as connected with the nucleus isthmi in all animals in which 

 that nucleus is well developed; but in urodeles this tract is very large, 

 though the nucleus isthmi is vestigial. 



4. Tecto-hulbar and tectospinal tracts. — These tracts have been 

 described and illustrated in the papers of 1936 (p. 340) and 1942 



