262 C. JUDSON HERRICK 



16. Tr actus preoptico-intercalaris 



The pars intercalaris diencephali is related with the nucleus 

 preopticus by a slender tract of unmyelinated fibers which will 

 next be described. In a single series of transverse Golgi sec- 

 tions almost the entire course of this peculiar tract can be fol- 

 lowed with perfect distinctness. It appears first at the level 

 of the optic chiasma as three slender fascicles in the stratum 

 album of the nucleus preopticus (fig. 15, tr.po.i.) and can be 

 followed in successive sections caudad and dorsad to its termina- 

 tion by free endings in the pars intercalaris (figs. 16 to 20). The 

 origin of these fibers from their cell bodies has not been observed, 

 but in a transverse section of a different specimen a single wisp 

 of similar fibers is found leaving the stratum griseum of the nu- 

 cleus preopticus (fig. 25, tr.po.i.), which probably represents 

 the portion of that tract which is missing in the other series and 

 is provisionally so labelled in the figure. This tract seems to 

 be comparable with the tractus olfacto-habenularis from the 

 preoptic nucleus to the habenula. 



17. Tractus hahenulo-peduncularis 



This tract, the fasciculus retroflexus of Meynert, pursues a 

 typical course from the habenula to the interpeduncular nucleus. 

 The , tract is unmyelinated, but myelinated fibers of diverse 

 sorts are added to it from the thalamus and other parts. For 

 the first part of its course the fibers run nearly horizontally 

 under the extensive pars intercalaris diencephali, then they turn 

 ventrally in a course parallel with the fibers of the posterior 

 commissure but farther rostrally (figs. 3 to 9, 28, 29, 30, 39, 

 41, 44, 46, 47, 49, 58, 59, 60, 63, 64, QSJ.retr.). They distribute 

 chiefly without decussation, in the interpeduncular nucleus, 

 both before and behind the fovea isthmi and far caudad under 

 the motor tegmentum (fig. 61). 



