FLOUNDER-FISHES. 
365 
alteration or none at all, and the parts of the brain 
retain their original position in the skull, while in most 
cases the palatine teeth, and sometimes the jaw -teeth 
as well, remain almost unchanged. 
Fig. 101. Skull of Pleuronectes platessa, 1 times the natural size. 
v, vomer; fr. a. d , right, fr. a. s, left lateral ethmoid bone; fr. d, right, 
fr. s , left frontal bone, the anterior parts of these bones being pressed 
forward to the right, and marked in the same way. 
sal tin, or at all events its predecessor, the embryonic 
vertical tin, extends so far forward on the dorsal edge 
of the head that the eye must force its way under the 
base of this tin, apparently straight through the head. 
e 
Fig. 102. Schematic figure of the skull of Pleuronectes platessa , 
borrowed from Traquair, as an explanation of the position of the 
various bones in the preceding figure, e, ethmoid bone; fr. a. d, right, 
fr. a. s, left lateral ethmoid bone, each pierced with a hole to receive 
the olfactory nerve; fr. d, right, fr. s, left frontal bone. — The un- 
shaded parts of these bones on the left indicate their secondary ex- 
crescences. — fr. p. d, hind frontal bone on the right, fr.p.s, on the 
left; p. cl, right, p. s, left parietal bone; o. s, upper occipital bone; 
mast, d, right, mast, s, left mastoid hone; squ. d, right, squ. s, left 
squamosal bone. The line oa shows the original dorsal edge of the 
skull, ox the secondary one. oc. d, right, oc. s, left eye. 
Fig. 103. Young Sole (Solea vulgaris), 12 mm. long and 4 1 mm. deep. After Malm, x — y, that part of the future base of the dorsal 
fin under which the left (upper) eye has probably passed; z, the optic lobes of the brain. 
These are the ordinary changes during the passage 
of the one eye from one side of the body to the other; 
but there are certain forms of Flatfish (among them 
probably the common Sole, fig. 103) in which the dor- 
This is the course of the wanderings of the eye in the 
transparent, perfectly clear Flatfishes — probably im- 
mature forms of species not yet fixed — which Steen- 
STRUP and A. Agassiz (see above) have figured and 
