238 C. JUDSON HEREICK 



calaris diencephali and accompany the tractus habenulo- 

 peduncularis, or fasciculus retroflexus of Meynert. 



The epiphysis envelopes the commissura habenularum dorsal- 

 ly and nerve fibers leave the epiphysis, not only at its attach- 

 ment behind the commissure, but also in smaller numbers 

 farther rostrally. The last was observed only on one side, the 

 fibers of this rostral root passing from the epiphysis into the 

 rostral border of the commissura habenularum, thence laterally 

 and slightly rostrad to the rostral surface of the habenula, where 

 they' turn ventrad. At lower levels these fibers turn ventrad 

 and join the larger second root. The larger bundle of fibers 

 forming the second or middle root of the parietal nerve is com- 

 posed of very coarse deeply staining myelinated fibers and 

 passes from the epiphyseal stalk into the habenula immediately 

 caudally of the habenular commissure, then descending through 

 the substance of the habenula. At the level where the tractus 

 habenulo-peduncularis leaves the caudal border of the habenula 

 these fibers accompany it and are immediately joined by the 

 .'fibers of the first root. 



The commissura tecti diencephali is extended forward through- 

 out the whole length of the pars intercalaris of the diencephalon 

 and thus comes almost into contact with the place of attach- 

 ment of the pineal stalk. The fibers of the third root of the 

 parietal nerve pass backward crossing at right angles the fibers 

 of the commissura tecti but none of them were seen to decussate 

 in the commissure. It is probable that none of the fibers of 

 the parietal nerve decussate in either the conmnissura habenu- 

 larum or the commissura tecti diencephali. 



The fibers of the parietal nerve can be followed ventralward 

 accompanying those of the tractus habenulo-peduncularis (which 

 is wholly unmyelinated in Necturus) across the massive emi- 

 nence which underlies the pars intercalaris of the roof (Schalt- 

 stiick) and to which I shall give the same name (figs. 63, 64, 

 65 p.i.th.). Some of these fibers may end in the habenula and 

 others in the pars intercalaris, but others certainly turn ventral- 

 ly with the tractus habenulo-peduncularis. Their ultimate 

 destination has not been determined, for they become mmgled 



