198 
FLOUNDER. 
from the origin of the dorsal fin forward, and this has been 
accompanied with a black surface below; but it seems probable 
that this greater frequency of variation is only because the 
fish itself is more frequently caught than other species of the 
family of flatfishes. The yellowish spots which sometimes mark 
its sides are very different from those which adorn the surface 
of the Plaice. 
But as regards the variety (here figured) which is marked 
with a notch or deficiency in the outline behind the eyes, 
and a black surface on the under side, it has occurred so 
frequently in some districts as to have raised the suspicion of 
its being truly a distinct species, the more especially as some 
difference in the fins has also been detected. But after 
comparing an example from the River Fowey with a specimen 
of Flounder of regular formation, I feel no doubt of their 
being specifically the same; while, on the other hand, I feel 
equally certain that this variety of structure in the outline is 
natural, and not, as has been supposed, the consequence of 
mutilation. 
Some observations which have been made on the structure 
of the mouth and checks of this fish are probably applicable, 
with a little variation, to the other flatfishes already described; 
for the want of symmetry, which is the character of this 
family, extends to all the tissues or portions of the head, 
including the nerves of feeling as well as the muscles and 
bones, and thus creating in the upper sui-face a far higher 
degree of power and sensibility than exists in the lower. Thus, 
what appears to be the largest nerve in the body is seen to 
pass along the coloured side of the cheeks, to be distributed 
to the palate, in comparison with which there does not appear 
to be any one on the lower side, while there is another here 
situated which passes down to supply the angle of the jaw. 
On the coloured side the (masseter) muscle of the jaw is 
strong, and is united to that bone by a tendon, which is not 
the case on the white side; and a separate nerve, somewhat 
corresponding to that already mentioned on the white side, is 
given out from the skull proportionally further forward, fl-om 
whence it descends under the tendon to the jaw, both these 
nerves being accompanied with blood-vessels. 
