218 FREDERICK TILNEY 
of the infundibular process and the exclusion from it of any acces- 
sory recess of third ventricle have progressed to the most extreme 
degree, for in these forms even the stem of the process is solid. 
In this way through a series of changes from the ichthyopsid 
to the mammal the evolution of the infundibular process may be 
traced. In this series the sauropsid condition still bears evidence 
of the saccus-formation in its apparently retrograding saccular 
surface; the conditions in the Felidae carry this retrograding 
process one step further toward the general mammalian type of 
infundibular process from which the saccular surface and the 
saccus-formation have entirely disappeared. 
It is not, however, until the entire floor of the ventricle is 
considered that the significance of each of its several parts may 
be ultimately determined. These parts have been designated 
by many terms, several of which have been devised with the 
intention of giving a phylogenetic or embryological interpreta- 
tion to the structures. Such, for example, is the case with the 
_ part described by Retzius (9) as the eminentia saccularis, for 
this term as applied to mammals imputes a genetic relationship 
between the eminence so described and the saccus vasculosus 
of fish. "That such a relationship does not actually exist can, 
I think, be proved. For these reasons in considering this region 
of the brain it seems advisable to employ such terms only. as 
shall be morphologically or topographically descriptive. To 
this end the following suggestions are offered for the structures 
found upon the floor of the third ventricle, beginning at the optic 
chiasm and proceeding caudad to the mammillary bodies: 
1. The optic chiasm. 
2. The supraoptic crest, a transverse ridge extending across 
the dorso-cephalic surface of the optic chiasm and for a short 
distance upon the optic nerves. 
3. The post-chiasmatic eminence, a marked protuberance of 
the floor immediately caudad to the chiasm; this structure is 
often referred to as the bulbus infundibult. 
4. The infundibular process, an expanded appendage to the 
floor connected with the infundibular bulb by the infundibular 
stem. ’ 
