WILLIAMS: MIGRATION OF EYE IN PSEUDOPLEURONECTES. 25 
There is also indicated at this stage a beginning of the forward rotation 
of the dorsal margin of the ect-ethmoid cartilages about a transverse axis 
passing through them. The end of the bristle (Fig. C) over the trabec- 
ulze cranii is, therefore, not greatly posterior to the outer end, which is 
seen against the left pterygo-palatine as a background. The final result 
of this rotation of the ect-ethmoids about the axis connecting them is to 
make the axes of both foramina transverse instead of longitudinal. Con- 
sequently in an oblique view from the right side, as in Figure D, one is 
looking at the olfactory foramina from that face of the ect-etlmoids 
which at an earlier stage (Figs. A, 6) was directed posteriad. Instead, 
therefore, of seeing the ends of the olfactory nerves which are distal to 
the foramina, as would be the case if the cartilages were viewed from 
the same direction at an earlier stage (Figs. A, 6, and C’) one would 
now see their proximal ends. 
A twisting of the ethmoids (in a clockwise direction when viewed 
from behind) about the antero-posterior axis of the fish, greater than is 
indicated in Figure C, results in the further elevation of the ect-ethmoid, 
olfactory foramen, and pterygo-palatine of the left side, while the supra- 
orbital, the ect-ethmoid, the olfactory foramen and the pterygo-palatine 
of the right side are correspondingly depressed. 
e. Stage LIV. 
The oldest facial region modelled (Fig. D)—that of a small fish 
(Plate 1, Figs. 5, 6) having the eyes in the adult position — represents 
my Stage IV. 
The eyes are located one on each side of the flat hook-like plate of 
cartilage (Fig. D, ham. eth.) which, with the previously mentioned 
median arch (are. eth. m.), runs back along the morphologically median 
plane (the plane between the eyes). The interorbital septum of con- 
nective tissue is continuous with these two cartilaginous processes, filling 
the space between them and extending thence backward. That this 
occupies the morphologically median plane, is proven by the position of 
the olfactory nerves, which lie one on each side of this septum. Ante- 
-riorly the left nerve passes through the opening (for. olf. s.) seen in the 
left (now upper) wing of the ethmoid and ends in the nasal capsule, 
which lies immediately in front of it. The right nerve comes from be- 
low the hook-shaped cartilage and passes through a foramen (for. 
olf. dx.) in the anterior part of the ethmoid to the right nasal capsule, 
which is located somewhat in front of the ethmoid and near the anterior 
end of the right pterygo-palatine. 
