246 FISH. [Vol. X. 



open to some question. The conclusion is that the olfactory 

 segment arose from a single median plate. His (18) proposes 

 the term angiihis terminalis believing that it has no connection 

 with the olfactory region. Wilder (58) has found in the human 

 brain "a subtriangular depression between the precommissure 

 and the two fornicolumns " which he calls the aulic recess. 

 From its mesal position in the terma and general form it is 

 quite suggestive of being a remnant of the primitive conditions 

 described by Kupffer, Rabl-Riickhard, and His in lower forms, 

 if the relations of the surrounding parts can be homologized. 



In the Desmognathus there is no very distinct ectal separation 

 of this segment from the prosencephal. The olfactory nerve 

 is attached along the ventro-lateral portion and may be cor- 

 related in some way with the greater lateral than mesal length 

 of this segment. Along this shorter mesal margin there is a 

 condensed aggregation of cells forming an ectocinerea ; this 

 occurs nowhere else in the whole brain, except perhaps at the 

 habenae ; there are also numerous cells scattered around the 

 attachment of the olfactory nerve. When the brain is divided 

 into frontal sections (Fig. 6) a very decided angle is noticeable 

 at about the middle of the length of the cavity of the cerebrum; 

 that portion from the angle cephalad is believed to have grown 

 away from its original direct communication with the aula as 

 noted by Mrs. Gage in Diemyctyhis larvae and to be the rhino- 

 coele or cavity proper of the rhinencephal. 



Prosencephal. — The prosencephal merges out of the pre- 

 ceding segment, growing wider caudad as the hemicerebrums 

 divaricate. The supraplexus is located at this angle of diver- 

 gence and on its entrance into the cavity divides into two main 

 branches (Fig. 3) the auliplexus and the diaplexus ; the former 

 sends off a branch into the cavity of the inf undibulum before 

 dividing to enter the paracoeles (lateral ventricles). The 

 diaplexus sends off a branch toward the epiphysis and then 

 passes caudad as far as the cerebellum. 



The terma in Desmognathus according to my interpretation 

 extends from the chiasma cephalad and then dorsad until it 

 reaches the supraplexus ; the dorsal portion is membranous — 

 a tela, and shuts off all communication of the mesal cavity with 



