MIDBRAIN AND THALAMUS OF NECTURUS 271 



The fascicles of this group begin rostrally in that dorsal region 

 of the motor tegmentum where the lateral forebrain bundle 

 spreads out and rapidly breaks up, and they end in the region 

 below the isthmus where the great descending bulbar systems 

 of fibers are beginning to form. Sagittal Cajal sections show 

 that the fascicles of the lateral forebrain bundle which enter 

 the rostral end of the tegmentum where these dorsal tegmental 

 fascicles arise are not continuous with them, but a synapse is 

 here interposed. It therefore appears probable that these 

 dorsal tegmental fascicles serve, in part at least, to transmit 

 nervous impulses from the basal forebrain bundle to the centers 

 of motor distribution in the medulla oblongata. 



23. The ventral tegmental fascicles 



These bundles, like the dorsal fascicles, arise within the pe- 

 dmiculus cerebri, but lie farther ventrally and are composed of 

 myelinated fibers. Many of their fibers, moreover, extend 

 farther caudad into the medulla oblongata, though large num- 

 bers end in the eminentia sub'cerebellaris tegmenti (figs. 9 to 

 14, 31, 32, 33, 35, 46, 47, 55, 68, f.v.t.). 



24.. Tr actus tegmento-hulbaris 



The eminentia subcerebellaris tegmenti receives the terminals 

 of the dorsal and ventral tegmental fasciculi, as already de- 

 scribed, including some endings from the fasciculus longitudi- 

 nalis medialis. Myelinated fibers are directed downward and 

 lateralward from this eminence into the reticular formation of 

 the medulla oblongata, the tractus tegmento-bulbaris (fig. 68, 

 tr.teg.b.). 



25. Fasciculus longitudinalis medialis 



This is a highly specialized member of the system of ventral 

 tegmental fascicles (figs. 7 to 14, 24, 29, 31, 32, 33, 46, 47, 49, 

 68, f.l.m.). Fibers of this system arise from neurons of the 

 nucleus of the tuberculum posterius and especially from a col- 

 lection of very large neurons scattered through the dorsal part 



