264 C. JUDSON HERRICK 



probably ultimately effect connections with other parts of the 

 motor tegmentum. Some of these fibers can be followed to 

 the region laterally of the nucleus of the III nerve (figs. 2, 3, 

 18, 25, 26, 27, 44, 45, 48, 49, tr.th.p.v.s.). Fibers of this system 

 also descend into the cerebral peduncle at intermediate levels 

 in company with the lateral forebrain tract (tractus thalamo- 

 peduncularis ventralis intermedins, figs. 25, 44, 48, tr.th.p.v.i.). 



The fibers from the pars dorsalis thalami and pars inter- 

 calaris are termed tractus thalamo-peduncularis dorsalis (fig. 

 68, tr.th.p.d.). These are chiefly unmyelinated and, as in the 

 preceding case, some are deep, some are superficial, and some 

 occupy intermediate levels. 



From the pars dorsalis thalami fibers which are chiefly un- 

 myelinated, with a few myelinated fibers among them, collect 

 and join the tractus habenulo-peduncularis in the deeper levels 

 of the stratum album. They can be followed to the region of 

 the tuberculum posterius. Other deep fibers take courses 

 farther ventrally and rostrally. All of these fibers belong to the 

 tractus thalamo-peduncularis dorsalis profundus (figs. 42, 43, 

 57, 58, tr.th.p.d. p.). 



There is also a rather compact fascicle of unmyelinated fibers 

 which passes ventro-caudad from the pars dorsalis thalami 

 in a superficial position (tractus thalamo-peduncularis dorsalis 

 superficialis) . Most of these fibers e^ddently connect with 

 the neurons of the nucleus of the tuberculum posterius and 

 others with neurons of the pars ventralis thalami; some may 

 also reach the pars dorsalis hypothalami. So far as observed 

 they are all uncrossed. Some slender strands of unmyelinated 

 fibers belonging to this tract come also from the nucleus of the 

 pars optica thalami. 



We may also consider here as belonging to this system a 

 very definite tract of fibers which arises in the pars intercalaris 

 of the diencephalon and passes ventrad and slightly caudad 

 along the extreme outer surface of the brain in the superficial 

 groove which separates the mesencephalon from the dien- 

 cephalon. These fibers are chiefly unmyelinated with a few mye- 

 linated fibers among them; they reach the ventro-lateral border of 



