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the right prefrontal retained its connection with the right 
frontal, but lost its connection with the parasphenoid bar. 
After the rotation of the orbital region the left prefrontal 
grew backwards and the left frontal forwards, so as to 
form the secondary junction of these two bones already 
referred to. 
(2.) The downward shifting of the oblique eye 
muscles from practically the frontal to the parasphenoid 
bar. This possibly began in the symmetrical but laterally 
flattened ancestor, as the frontals became attenuated from 
side to side and deepened dorso-ventrally. But it was 
continued in the asymmetrical fish. The object of the 
shifting of the eyes was to make dorsal vision possible 
with both eyes. In the Cod the origins of the oblique 
muscles are best adapted for lateral vision and for visual 
axes In approximately the same straight line. In the 
Plaice, however, the visual axes are directed dorsally, and 
to bring this about the oblique muscles had to shift 
ventrally so as to exercise a more effective pull over the 
eyes. The origins of these muscles therefore moved down- 
wards towards the ventral region of the cranium and 
ultimately to the parasphenoid bar. 
(5.) The attachment of all the oblique muscles to the 
left prefrontal. We have already pointed out that the 
right prefrontal has lost its connection with the 
parasphenoid bar. ‘This would doubtless have occurred in 
the earlier stages of the rotation of the eyes. When, 
therefore, in the final stages of the torsion, the oblique 
muscles in their downward passage over the interorbital 
septum arrived at the bar, the right prefrontal must have 
already left it. They thereupon continued their migra- 
tion on to the left side and became attached to the left 
prefrontal—the only convenient attachment remaining. 
(4.) The passage of the right oblique museles through 
