THE DIENCEPHALIC FLOOR pales 
portion into the lateral processes. At this stage, therefore, it 
is possible to distinguish between a dorsal or saccular surface 
and a ventral surface, the latter being in contact with the anlage 
of the pituitary gland. 
Dorsal to the stem of the infundibular process is a small evagi- 
nation corresponding in its general relations to the part already 
described as the anlage of the post-infundibular eminence (36). 
Its growth has been less pronounced than that of the other parts 
of the infundibular region. The cavity of the third ventricle 
extends into it forming the post-infundibular recess (35). In 
the mammillary region (25) the tendency toward the reduction 
of the ventricular cavity already noted in the chick of eight 
days has proceeded still further. The mammillary region itself 
forms a large protuberance dorsal to the post-infundibular emi- 
nence. The lateral median evaginations are still prominent on 
the surface, but the cavities contained in them have been greatly 
reduced now forming small accessory recesses connected with 
the third ventricle. The median mammillary recess (26) is 
still prominent sagittally, although its transverse diameters 
are much reduced. The mammillary bodies are now defined 
upon the surface. 
Chick of fourteen days, eighteen hours; Specimen No. 1418 
(fig. 21). In this stage adult conditions have practically been 
attained. The post-chiasmatic eminence (32) is less prominent 
with the result that the prechiasmatic recess (38) is less well 
defined. ‘Traced laterad, however, this recess may be followed 
into a small canal overlying the chiasm and proximal portion 
of the optic nerve, the supraoptic recess (42). The position of 
this recess is marked upon the surface by the supraoptic crest 
(41). In the infundibular region the post-chiasmatic eminence 
is well defined; its median post-chiasmatic groove (23) as 
well as its two lateral processes are prominent. The caudal 
portion of the infundibular region shows but little change. The 
main portion of the infundibular process is somewhat larger; 
its dorsal convoluted surface is in even greater contrast to the 
ventral pituitary surface because of its more marked convolution. 
The third ventricle communicates with the infundibular process 
