274 DR. TRAQUAIR ON THE ASYMMETRY OF THE PLEURONECTIDJA. 
more developed, forming more than one-half of the inner wall of the orbit, while the 
interocular process is reduced to a mere curved spiculum (m, fig. 11), passing all round 
the outer margin of the orbit, closely applied to the stouter interocular process of the 
other frontal bone. A ridge continued from the supraoccipital bone passes over the 
frontal of the eyeless side, and on to its external angular process; it supports the 
cephalie continuation of the dorsal fin. 
Anterior Part of the Head.—The Cartilage (Plate XXIX. figs. 8-10, a).—This is 
thinner and smaller than in the Turbot, but its shape and relations are analogous. 
Its upper border is divided by two notches into three very unequal processes, of which 
that on the ocular side, by far the largest, extends posteriorly, and supports the process 
(a) of the prefontal of the ocular side. Into the larger notch (g) on the ocular side is 
inserted the extremity of the interocular process of the frontal of the same side; and 
into the smaller notch (2) on the other side is inserted the extremity of the correspond- 
ing part of the frontal of the eyeless side, in the manner represented in Plate XXIX. 
fig. 8. This cartilage, then, as in the Turbot, is very unequally developed Fig. 3. 
on its two sides, the side corresponding to the eyeless side of the fish ap- 
pearing as if quite atrophied—corresponding with the small size of the in- 
terocular process of the frontal and the complete non-development of the 
process (4) of the prefrontal of the eyeless side (see p. 272). 
Vomer (1).—This bone appears twisted on its long axis up towards the eyeless side, 
as in the Turbot, but in a more exaggerated degree (see Plate XXX. fig. 3, where the 
vomer is seen from the front). Anteriorly it presents two articular facets (p & 4 
figs. 8, 9, Plate XXIX.), of which that on the eyeless side (p) is larger, Fr 
and looks more laterally than the opposite one (q); a line bisecting : 
the angle formed by these two facets would pass obliquely towards the 
eyeless side, as in the adjoining diagram. The lateral ala on the eyeless side, 
besides being larger, and directed more vertically upwards, is also directed 
more posteriorly than the opposite one; so that the bone, in addition to 
being twisted on its long axis upwards and to the eyeless side, has that 
axis turned to the eyeless side at its extremity, as indicated by the dotted line in the 
diagram. The full import of this will be seen when we consider the bones of the face. 
Nasal.—The prominence (4) on which the intermaxillary cartilage glides is obliquely 
directed towards the eyeless side. The nasal bone in the Halibut is more expanded | 
transversely than in the Turbot, and thus comes to enter into the boundary of the orbit 
(Plate XXIX. figs. 8&10, ıs). It is also apparent that this increase of size transversely is 
chiefly due to development on its eyeless side. 
Prefrontals (ws), These are more nearly of the same size as in the Turbot, though that 
ofthe eyeless side is still a good deal larger than its fellow. I have already alluded to me 
‚fact that in the Turbot the process (a) of the prefrontal of the ocular side, which articu- 
lates with the interocular process of the corresponding frontal, is not at all developed in 
wiegen of the eyeless side, an interval filled by cartilage (s, Plate XXIX. we 
T di ween the frontal and prefrontal anteriorly on. that side. In the Hat ji 
preirontal of the eyeless side, at the place where the process (a) should be given °> 
