THE DIENCEPHALIC FLOOR 279 
CONCLUSIONS 
The supraoptic crest, chiasmatic process, prechiasmatie and 
supraoptic recesses in the mammal have their definite homologues 
in the sauropsid and ichthyopsid. 
Of the structures derived from the ventral segment of the 
ectoptic zone the post-chiasmatic eminence of the mammal and 
bird may be homologized with the inferior lobes or hypoarium 
of fishes, while there is some evidence which seems to indicate 
that the eminentiae laterales hypencephali are the homologues 
of the lateral lobes of teleosts. 
The derivatives of the caudal portion of the infundibular region, 
including its apex, are the infundibular process and post-infundib- 
ular eminence. 
The infundibular process in the selachian presents a pituitary 
and a saccular surface, the latter forming the saccus vasculosus. 
In the bird these two surfaces are present; the saccular surface, 
although it has some of the characteristics of a saccus-formation, 
does not present an actual saccus vasculosus. So far as may now 
be stated for the condition in mammals, the Felidae present an ex- 
tensive pituitary surface in their infundibular process. The saccu- 
lar surface, however, has lost all characteristics of saccus-formation 
and is in fact invested by tissue of the pituitary gland. In other 
mammals it is difficult to draw distinction between the pituitary 
and saccular surfaces of the infundibular process, and this 
differentiation in Mammalia would indeed be impossible were 
it not for the intermediate position of the Felidae in this respect 
between the bird, on the one hand, and the majority of mammals 
on the other. The lateral extensions of the infundibular process, 
the infundibular recess, infundibular stem and infundibular 
canal of the domestic cat all have their homologues in the bird 
and selachian. The disappearance of the saccus vasculosus 
from the mammal may be traced through several stages of 
retrogression from the dog-fish to the cat, so that the homology 
of the infundibular process as a whole in the mammal with that 
of the selachian seems to be warrantable. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, NO. 3 
