1 62 Journal of Comparative Neurology. 



and posiparapJiysis of Herrick do not seem to be structures at all 

 comparable. The extent of the diatela in Nechinis appears to 

 be due simply to the elongated condition of the brain ; the su- 

 praplexus extends cephalad closely applied to the roof connect- 

 ed with the dura. The velum extends ventro-caudad, forming 

 dorsad of it the apparent evagination. 



Plexuses. — The plexuses of the prosencephal and dien- 

 cephal are greatly developed in Necturus ; the relations, how- 

 ever, are as Mrs. Gage has shown in Diemyctyhis, and the names 

 applied by her are here adopted. The aidiplexiis intrudes into 

 the cavities cephalad of the parapJiysis. It sends extensions 

 through the port as intothe paraccele and another division caudad 

 into the infundibulum. The diaplexus arises from the velum 

 and the diatela and extends caudad to the cerebellum, occa- 

 sionally protuding caudad of it into the metacoele. In the larva 

 the plexuses are much simpler than in the adult, and the rela- 

 tions set forth above are much more easily seen. 



On the dorsal edge of the divaricated walls cephalad of the 

 supracommissure are situated the habenas. Caudad ofthesupra- 

 commissure in a similar position and extending almost to the 

 postcommissure is another nidus of cells similar to those of the 

 habenas probably representing Meynert's nidus, since Meynert's 

 bundle seems to spring from here. Dorso-caudad of the portas 

 lie the cell areas from which spring fibers which join the dorsal 

 cerebral commissure. This is molded about a core of alba 

 from which the fibers arise, and is bounded dorsally by a well 

 marked sulcus, which extends caudad, growing fainter to again 

 become distinct in the caudal region of the diencephal. On the 

 floor of the brain caudad of the cerebral commissures is the 

 cephalic projection of the cavity, the preoptic recess, from the 

 caudal portion of which and cephalad of the chiasma the optic 

 recesses project laterally to constitute the lumen of the hollow 

 optic nerve, as already mentioned. The infundibulum, as in 

 other urodeles, is large, extending caudad so as to completely 

 conceal the mesencephal. The hypophysis is attached to the 

 caudal end of the infundibulum, whose cavity extends dorsad of 

 it as the saccus vasculosus. 



