THE DIENCEPHALIC FLOOR 261 
ventricle extends from the narrow median portion of the post- 
chiasmatic eminence into the two lateral processes, thus forming 
the recessus lobi inferioris. From the dorsal region of the 
pituitary anlage two sprouts, each as yet independent of the 
other, are growing forward along the ventral surface of the median 
post-chiasmatic groove. 
Mustelus of 50 and 70 mm.; Specimens Nos. 725 and 735 (figs. 27 
and 28). The development in these stages has carried the differ- 
44 
Fig. 27. Mesial view of forebrain reconstruction of 50 mm. Mustelus. X 50. 
The unshaded area shows the cut surfaces of the reconstruction. 2, chiasmatic 
process; 4, chiasm; 7, epiphysis; 13, infundibular process; 24, mid-brain; 25, 
mammillary region; 32, post-chiasmatic eminence (lobus inferior) ; 33, post-chias- 
matic recess (recess of inferior lobe); 36, post-infundibular evagination; 39, 
paraphysis; 4/, supra-optic crest; 42, supra-optic recess; 44, telencephalon; 47, 
velum transversum. 
