186 
It is very remarkable that comparatively slight 
changes would have sufficed to bring about the distortion 
of the Plaice’s skull starting with such conditions and 
tendencies as we have indicated above. In the head of 
the Plaice the orbital region only has suffered extensive 
change. The otic region has undergone practically no 
change, and the prefrontal region certainly less than the 
orbital. The jaw apparatus is not affected at all by the 
torsion of the orbit, but has an asymmetry of its own (as 
described above), and this latter doubtless explains the 
asymmetry of the prefrontal region, which is of a different 
character to that of the orbital. We have, therefore, now 
to consider whether such relationships in the anatomy of 
the skull and eyes as obtain in the Plaice can be reason- 
ably expected to have followed from such a course of 
evolution as we have sketched above. There appear to us 
to be four difficulties requiring explanation. ‘These are 
as follows : — 
(1.) The relations of the two prefrontals. As the 
right frontal bent over further to the right side, the right 
eye would be forced downwards. ‘To make room for it 
the parasphenoid bar most probably bent over to the left 
to the position in which we now actually find it. The pre- 
frontal region lagged behind in this shifting, being 
unaffected except as regards the movements of the adja- 
cent parts (orbital region and jaw apparatus). If a Cod’s 
skull be examined it will be seen that the abortion of the 
left frontal would result in the separation of the left 
prefrontal from the remainder of the frontal area, and 
further that the greater rotation of the frontal over the 
prefrontal area would result ether in the separation of the 
right prefrontal from the right frontal, or in its separation 
from the parasphenoid bar. Now the latter having itself 
rotated to the left, we therefore find that in the Plaice 
