The Brain of Diemydylus Viridescens 281 



INFONDIBDLUM. 



Since the investigations of Miiller in 1871, not much of fun- 

 damental importance has been added to the knowledge of this 

 region. It is thought desirable here to compare the extreme 

 variation in position of homolgous parts and to contrast the 

 simple and complex character of the region in different forms. 

 It seems that to give these parts collectively the name of a 

 lobe as has been done is misleading, but that the term, infun- 

 dibulum, long employed, may be used, apart from its strict 

 etymological significance, with reference to the whole region 

 and its appendages. 



In the amia a cephalic projection of the cavity is associated 

 with the hypophysis (Fig. 93, 98) as is also the case with 

 lamprey (Fig. 103). In diemyctylus the whole infundibulum 

 extends caudad but the hypophysis is associated with the part 

 next the chiasma (Fig. 6). 



In amia from the caudal part are four projections of the 

 cavity (Fig. 93, 100) ; the two dorsal are symmetrical, and 

 extend into the hypoaria ; next a mesal cavity, short in ex- 

 tent ; ventrad a longer extension, the saccus, with walls of 

 different structure, apparently non nervous. In lamprey only 

 one caudal process exists (Fig. 103, 108), while in diemycty- 

 lus the relations are obscure. There is a small lobular process 

 which in position corresponds with the saccus but the mem- 

 branous wall dorsad of it more nearly in structure resembles 

 the saccus (Fig. 6, 50). 



CEREBRAL COMMISSURES. 



The variations in position of these commisures both with re- 

 lation to the brain masses and to each other seem to present one 

 of the most puzzling problems to be solved in comparative neu- 

 rology. The work of Reissner (42) and especially of Osborn 

 (38) in determining the existence and relations of the callosum 

 in im-mammalia clearly showed these variations, the position 

 of the callosum and precommissure in urodeles being much 

 more like that in fishes than in anura. In the latter the con- 

 ditions are not dissimilar to those shown by Marchand (31) as 



