MIDBRAIN AND THALAMUS OF NECTURUS 293 



of the commissura tecti mesencephali and the commissura 

 posterior, the tractus tecto-peduncularis, and probably some 

 fibers from the tractus tecto-thalamicus et hypothalamicus 

 cruciatus; fibers from the habenula by the tractus habenulo- 

 peduncularis ; a few fibers of the parietal nerve (these may be 

 efferent in function); fibers from the pars intercalaris, the pars 

 dorsalis, and the pars ventralis of the diencephalon by the 

 tractus thalamo-peduncularis ; fibers from the pars dorsalis 

 thalami by the tractus thalamo-hypothalamicus et peduncularis 

 cruciatus; fibers of the nervus terminahs (these may be efferent 

 in function) ; fibers from the lateral walls of the cerebral hemi- 

 spheres by the lateral forebrain bundle; fibers from the medial 

 walls of the cerebral hemispheres by the medial forebrain bundle ; 

 fibers from the hypothalamus which have not yet been fully 

 analyzed. 



The known efferent connections from this region (including 

 the tegmentum both above and below the fovea isthmi) are as 

 follows: the peripheral neurons of the III and IV nerves; possibly 

 fibers of the nervus parietalis and nervus terminalis; the fas- 

 ciculus longitudinahs mediahs; the tractus pedunculo-bulbaris. 

 The dorsal and ventral tegmental facicles (p. 270) arise and 

 terminate within the region here under consideration. They 

 conduct descending impulses into the eminentia subcerebellaris 

 tegmenti, and after a synapse here into the medulla oblongata. 



I have been able to demonstrate very few fibers of passage 

 in Necturus, which traverse the cerebral peduncle without 

 effecting functional connections either mthin it or within the 

 eminentia subcerebellaris tegmenti. Some fibers of the lateral 

 forebrain bundle and of the tractus tecto-thalamicus et pedun- 

 cularis cruciatus may extend beyond the limits of these struc- 

 tures into the medulla oblongata, but most fibers of even these 

 systems are interrupted by a synapse in the motor tegmentum 

 under the tectum. On the other hand, the fibers of both the 

 direct and crossed tractus tecto-bulbaris pass uninterruptedly 

 through into the medulla oblongata. 



The fiber tracts of the motor tegmentum which have been 

 described in the preceding paragraphs are arranged in the 



