MIDBRAIN 217 



The gray layer is relatively thin, and in the mid-plane most of its 

 cells are displaced by the massive decussations of the commissure of 

 the tuberculum posterius (figs. 2C, 29, 30, 31, 94). More laterally, 

 large and small cells are mingled in the gray, with little evidence 

 of local segregation except for the nucleus of the oculomotor nerve 

 at the posteroventral border. 



The largest cells include dorsally the primordium of the nucleus of 

 Darkschewitsch, which is related primarily with the posterior com- 

 missure (figs. 6, 18, '2'2, 24; shown but not named in fig. 32), more 

 ventrally Cajal's interstitial nucleus of the f. longitudinalis medialis 

 (figs. 18, 22, 104), and posteriorly the III nucleus (figs. 18, 22, 24, 93, 

 104). Larval forms of these cells have been illustrated ('396, figs. 42, 

 53, 72, 73). They resemble those of Necturus ('17, figs. 23, 24, 30, 33). 



These cells evidently are collectors of a wide variety of nervous 

 impulses brought into the peduncle by the numberless fibers which 

 converge to end here and by fibers of passage with collaterals in this 

 area. The axons of these cells descend in the ventral tegmental fasci- 

 cles and seem to be primarily concerned with activation of mass 

 movements, particularly of locomotion. Most of these thick fibers 

 descend in ventral tegmental fascicles of group (5) and are uncrossed, 

 but some of them decussate in the ventral commissure, mingled with 

 the tecto-bulbar fibers of the ventral median fascicles of group (1) 

 ('396, figs. 23, 24). 



Small cells in the anteroventral part of the peduncle are intimately 

 connected with the underlying hypothalamus and are doubtless con- 

 cerned primarily with olfacto-visceral adjustments (figs. 18, 21, 53). 

 There are numberless terminals here of the nervus terminalis, tr. 

 hypothalamo-peduncularis from the ventral hypothalamus ('42, p. 

 226 and figs. 3, 22, 23, 68, 69), tr. mamillo-peduncularis from the 

 dorsal hypothalamus ('396, fig. 22; '42, fig. 39), and tr. olfacto- 

 peduncularis from the anterior olfactory nucleus and primordial head 

 of the caudate nucleus ('396, fig. 1). This area also receives terminals 

 of the secondary and tertiary visceral-gustatory tracts, and there is a 

 strong pedunculo-hypothalamic connection (fig. 8; '42, p. 227). Ven- 

 tral tegmental fascicles (3) and (4) from the hypothalamus ('42, fig. 

 3) are related with this area ('42, figs. 39, 40, 44), and these fascicles, 

 together with the related small cells, probably contain primordia of 

 those components of the mammalian dorsal longitudinal fasciculus of 

 Schutz which are related with the peduncle and hypothalamus 

 (Thompson, '42, p. 249). 



Cells of medium size at the posterior end of the peduncular gray in 



