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the ethmoid fenestra. Primitively these muscles did not 
pass through a fenestra. In the Cod’s cranium this does 
not exist, but there is a cartilaginous wall in front of the 
origin of the oblique muscles. In the migration ventrally 
of the origins of these muscles the latter passed behind 
and across to the left of the ethmoid cartilage to reach the 
left prefrontal. The former then grew up behind and 
over the muscles, thus forming the fenestra. 
We have not studied the anatomy of the head in 
other Pleuronectids, and are unable to say whether the 
relations of the eye muscles above described are general. 
Cunningham (op. ct.) has described those relations in the 
sole, and it appears that they differ considerably from 
those we find in the Plaice. In the sole “the superior 
oblique of the ventral [right] eye arises from the small 
left [right is evidently meant] ectethmoid which is on the 
right edge of the interorbital septum; the inferior oblique 
arises from the external surface of the parasphenoid below 
the right ectethmoid. But both oblique muscles of the 
left or dorsal eye arise from the inner surface of the left 
ectethmoid.” Owing to this disposition the direction of 
the oblique muscles of the left eye is at right-angles to 
that of those of the right, and this difference has resulted 
from a rotation of the left ectethmoid. 
The asymmetry of the sole was produced according to 
Cunningham by the constant contraction of the oblique 
muscles of the left eye, so as to “ turn the pupil into a 
horizontal direction and look along the edge of the head.” 
The eye thus pressed on the interorbital septum, and led 
to the absorption and distortion of the latter. At the 
same time the fulerum of this pull (the left ectethmoid) 
has itself undergone considerable rotation ‘‘so that the 
surface of attachment [of the oblique muscles] which 
originally looked outwards to the left came to look upwards.”’ 
