SEA-FISHERIES LABORATORY. 333 



In the absence of figures we find it difficult to follow 

 Cunningham's explanation, and we also find it difficult 

 to believe that the same mechanical strain — that of the 

 oblique muscles between the left ectethmoid and the left 

 optic bulb — could have, at the same time, (1) rotated the 

 bulb, (2) pressed on the interorbital septum so as to bend 

 that over to the right, and (3) rotated the ectethmoid 

 through a right angle. And we regard it as unjustifiable 

 to base such a mechanical explanation on the attachments 

 of the muscles in an already asymmetrical skull. It is 

 inconceivable that the oblique muscles were attached in 

 the immediate symmetrical ancestor of the sole in the 

 same way that they are now. In the Cod, for example, we 

 find them arising symmetrically from the interorbital 

 septum, and therefore any discussion of the possibility of 

 those muscles producing distortion of the head should be 

 based on the conditions present in an unmodified 

 symmetrical cranium. 



But whatever the conditions are in the sole we find 

 that in the Plaice Cunningham's hypothesis is an impos- 

 sible one. Unlike the sole, all the oblique muscles are 

 attached to the left prefrontal ( = Cunningham's left 

 ectethmoid), and the latter we regard as the least altered 

 element in the orbital or preorbital regions. That the 

 surface to which the oblique muscles are attached now 

 looks upwards we regard as more simply explained by 

 supposing that the upper portion of the left prefrontal like 

 most of the left frontal, with which it was most probably 

 suturally attached, suffered abortion in the shifting of the 

 left eye. And the shifting of the origins of the oblique 

 muscles to it has been a result of, or has been concomi- 

 tantly brought about by, the approximation of the eyes, 

 and the increasing tendency to dorsal vision. 



