MIDBRAIN AND THALAMUS OF NECTURUS 239 



with other myelinated fibers belonging to the tractus thalamo- 

 peduncularis dorsalis which come from, the pars dorsahs thalami. 



In the sagittal series stained by Weigert's method the same 

 relations were found as in the horizontal series, including the 

 small first root entering the brain in front of the habenular 

 commissure on one side. Fibers of the parietal nerve near the 

 median plane are mingled with those of both the commissura 

 habenularum and the commissura tecti diencephali, but none of 

 ttiem decussate in these commissures. At the dorsal surface 

 of the brain the parietal nerve is represented by several fascicles 

 each containing about six heavily myelinated fibers, which 

 farther ventrally converge to join the unmyelinated fibers of 

 the tractus habenulo-peduncularis. They can be definitely 

 followed ventral ward for about half the length of the latter 

 tract, and probably reach the cerebral peduncle, though this 

 cannot be positively stated. 



In the transverse Weigert series also these connections of 

 the parietal nerve are confirmed (figs. 1 to 7, n.par.). The 

 rostral root was not demonstrated, but the middle root passes 

 downward and joins the tractus habenulo-peduncularis, as in 

 the horizontal and sagittal series. It is joined farther cau- 

 dally by the third root in the same way. No decussating fibers 

 were seen. In this series also the nerve can be traced about 

 half of the distance between the habenula and the interpedun- 

 cular nucleus. 



From these incomplete observations it appears that the pari- 

 etal nerve of Necturus is composed of a small number of heavily 

 myelinated fibers running between the epithelium of the pineal 

 vesicle and a point dorsally of the tuberculum posterius near 

 the boundary between the pars ventralis thalami and the pedun- 

 culus cerebri or some point still farther ventrally. There is no 

 evidence of nerve cells or of any active sensory function in the 

 pineal vesicle. The nerve fibers here demonstrated are, there- 

 fore, probably not functionally equivalent with those of the 

 unmyelinated parietal nerve described by Dendy in Sphenodon. 

 From their connection vnth the motor lamina of the brain tube 

 it is suggested that they are probably efferent in function 



