33*2 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



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 (pp. cit.) 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 k 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 fulcrum 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." 



