THE DIENCEPHALIC FLOOR 257 
tinguished, the former manifesting as yet but slight cupping, 
the latter a definitely constricted stem attaching to the lateral 
wall of the forebrain. The prosencephalic ventricle extends 
through the optic peduncle into the spacious recess of the eye- 
cup. The vertical segment of the optic sulcus is not present, 
43 8 
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EERO RS ILI clo gly 
' Au aes 
Br | HOS CR CT 
ih finland 
yt 
rghit bee 
CORUNA 
45 
“LZ. 
(ane SS 
Z] 
A 
LIT777 
17 
Fig. 24 Mesial view of forebrain reconstruction of 7 mm. Mustelus laevis. 
< 150. The unshaded area shows the cut surfaces of the reconstruction. 8, 
ectoptic zone of Schulte; 17, infundibular region; 25, mammillary region; 28, 
neuropore; 29, optic evagination; 31, optico-infundibular groove; 43, thala- 
mencephalon; 44, telencephalon; 46, tubercle of the floor of Schulte. 
but the optico-infundibular groove (31) passes in the position 
of the horizontal segment of the sulcus from the orifice of the 
optic peduncle (29) ventro-caudally to the side of the floor 
tubercle (46). The infundibular and mammillary regions pre- 
sent little change in size. The tuberculum postero-superius 
(45) is not prominent. 
