226 FREDERICK TILNEY 
THE DIENCEPHALIC FLOOR OF THE ADULT FOWL (GALLUS GALLUS) 
All of the eminences appearing in the cat may be identified 
in the fowl (fig. 4). The supraoptic crest (47) is present as a 
ridge extending laterad along the dorso-cephalic border of the 
chiasm toward the optic nerve. It marks the position of the 
supraoptic recess (42) of the third ventricle. Caudad to the 
chiasm the diencephalic floor forms a prominent post-chiasmatic 
eminence (32) which, as in the case of mammals, is invested by 
the tuberal portion of the pituitary gland and contains the 
post-chiasmatic recess (33). From the caudal extremity of 
this eminence projects the infundibular stem (//) terminating 
in the infundibular process (1/3). In the bird and the reptile 
this process presents certain features which distinguish it from 
that of the mammal. It is broader and each lateral extremity 
is prolonged to form a slender lateral process (16) similar to the 
lateral process of the selachian. Equally characteristic are the 
two surfaces of the infundibular process, i.e., the pituitary (15) 
-and saccular (14) surfaces; the former is in contact with the 
pituitary gland; the latter has no such relation but presents 
many irregular convolutions. Its wall is thickand non-vascular. 
As the saccular surface of the infundibular process ascends and 
appreaches the general plane of the ventricular floor it becomes 
evaginated to form a diverticulum, the post-infundibular emi- 
nence (34). This structure seems to present features in which 
it differs from the post-infundibular eminence in the cat. It 
appears to be a constituent of the post-chiasmatic eminence 
rather than being directly in the floor of the ventricle as in mam- 
mals. In Botaurus lentiginosus (shown in fig. 5) it more 
closely resembles the mammalian conditions. The avian third 
ventricle is in general much more narrow than in other forms. 
Only in its cephalic extremity does it broaden out to establish 
free communication with the large prechiasmatic and _post- 
chiasmatic recesses. In the interthalamic portion of the ven- 
tricle in the fowl the walls are in close apposition; the extent of 
the cavity in this region is further limited by the unusual size of 
the tuberculum postero-superius which projects cephalad for a 
