THE DIENCEPHALIC FLOOR papas) 
formed has its surface expression in the post-chiasmatic eminence 
and consequently this portion of the ventricular cavity is the 
post-chiasmatic recess (33). This recess extends laterally on 
either side of the median line forming an expanded portion of 
the ventricular cavity. As it is followed caudad the post- 
chiasmatic recess becomes constricted until it forms a tubular 
canal, the infundibular canal (12), which passes through the 
infundibular stem to communicate with the cavity of the in- 
fundibular process, the recessus processi infundibuli (40). The 
post-chiasmatic recess and the infundibular canal were present 
in all the forms examined but the distance to which the canal 
penetrates the infundibular stem is variable. In the Felidae 
it passes through the entire length of the stem while in all other 
carnivores it extends a short distance only. It is shortest in 
ungulates, anthropoids and man, although in these forms the 
infundibular stem attains its greatest length. The recess of the 
infundibular process is present, so far as I am at present able 
to state concerning mammals, in the Felidae alone. In these 
forms it is in direct communication with the third ventricle 
through the infundibular canal. In such birds and reptiles as 
I have studied it is present as a cavity having numerous accessory 
diverticula. The general conformation of this recess and the 
infundibular process which contains it have already been dis- 
cussed (page 214). 
As the dorsal surface of the post-chiasmatic eminence (32) 
ascends and reaches the plane of the floor, it becomes continuous 
with an area whose external expression is the ventral surface of 
the post-infundibular eminence (34). Entally this area presents 
several transverse ridges which separate two or three rather well 
marked grooves extending transversely across the floor of this 
region. Caudal to these folds the floor-plate becomes smooth 
and laterally a conspicuous sinus or recess situated in front of 
the mammillary recess appears in all the mammals studied. Like 
several of the other structures already mentioned, it is a most 
conspicuous element in the Felidae. 
