270 C. JUDSON HERRICK 



and they lie ventro-medially of the more compact lateral fore- 

 brain bundle (figs. 1 to 5, 46, 55, 57, 58, f.med.t.). Johnston 

 ('15, p. 464, fig. 54) mentions that in turtles almost all of the 

 fibers of this tract enter the tegmentum of the midbrain in- 

 stead of connecting T\ith the hypothalamus as commonly de- 

 scribed. In Necturus most of these fibers clearly connect with 

 the hypothalamus; but some of them can be seen in parasagittal 

 sections to reach the ventral part of the tegmentum of the mid- 

 brain (fig. 55). Some such fibers are also seen in a horizontal 

 Golgi section (fig. 46.) These probably represent a tractus 

 olfacto-tegmentalis. Long dendrites of neurons of the hypo- 

 thalamus are mingled with these fibers, some of them extending 

 forward beyond the level of the chiasma ridge. 



The stratum album of the cerebral peduncle and motor teg- 

 mentum farther caudad receives the numerous tracts from the 

 tectum mesencephaU, from the diencephalon, and from the 

 telencephalon to which reference has already been made. In 

 addition to these there are numerous descending tracts which 

 :arise within this region. These intrinsic tegmental systems 

 fall into two groups, which are here called the dorsal and ven- 

 tral tegmental fascicles. All of the tracts of the cerebral pe- 

 duncle are enumerated on pages 292-297. 



22. The dorsal tegmental fascicles 



These comprise five clearly defined bundles of large size and 

 some smaller ones, whose fibers are largely, though not exclu- 

 sively, unmyelinated (figs. 10 to 14, 24, 33, 35, QS,f.d.t.). They 

 lie ventrally of the lemniscus systems and in the deeper layers 

 of the stratum album. When followed forward in transverse 

 Weigert sections these fascicles are seen to lose their individ- 

 uality at about the level of the tuberculum posterius (fig. 10). 

 When followed caudad they break up in the eminentia subcere- 

 bellaris tegmenti below the isthmus (fig. 14). Though our 

 preparations do not exclude the possibility that individual 

 fibers of these fascicles may extend much farther, the fascicles 

 as such clearly run between the nucleus of the tuberculum pos- 

 terius and the eminentia subcerebellaris tegmenti. 



