THE DIENCEPHALIC FLOOR Zo 
The infundibular process manifests a tendency toward the 
development of a short infundibular stem (/1) while at the sides 
it gives the first evidence of its lateral processes (16). The 
mammillary region presents two large lateral processes and a 
smaller median recess with surface markings corresponding 
with these evaginations. The mammillary recess (26) as a 
whole is gradually being reduced, due to a thickening of its 
lateral walls. 
24 - 
13 12 
Fig. 19 Mesial view of forebrain reconstruction of chick of 8 days. X 50. 
The unshaded area shows the cut surfaces of the reconstruction. 2, chiasmatic 
process; 3, cerebellum; 4, chiasm; 7, epiphysis; 9, foramen of Monro; 11, 
infundibular stem; /2, infundibular canal; /3, infundibular process; 16, infundib- 
ular process (lateral process); 24, mid-brain; 25, mammillary region; 26, mam- 
millary recess; 32, post-chiasmatic eminence; 36, post-infundibular eminence; 
38, pre-chiasmatic recess; 4/, supra-optic crest; 42, supra-optic recess; 44, 
telencephalon. 
Chick of nine days, nineteen hours; Specimen No. 919 (fig. 20). 
The reconstruction of this stage shows no material change in the 
supraoptic crest (417), supraoptic and prechiasmatic recesses 
(42 and 38). The chiasmatic process (2) is less prominent than 
in the eight-day chick, although the chiasm (4) has increased 
relatively in size. Caudal to the chiasm the post-chiasmatic 
eminence (32) has gained somewhat in prominence. It now 
