292 DR. TRAQUAIR ON THE ASYMMETRY OF THE PLEURONECTIDÆ. 
a. A process of the prefrontal of the eyed side, sent between the eyes to articulate with the interocular 
process (m’) of the corresponding frontal. 
b. A process sent downwards and backwards by the prefrontal of the eyeless side to articulate with 
the basi-presphenoid. 
Fig. 3. Upper aspect of the same cranium, the two frontals, the two parietals, and the anterior part of 
the supraoccipital being removed. The interior of the brain-cavity is thus partially exposed ; 
a bristle is passed through each olfactory foramen in the direction pursued by the olfactory nerve. 
g. À process of the cartilage (4) supporting the interocular process of the frontal of the ocular side, 
and the corresponding process (a) of the prefrontal of the same side. 
h. A smaller process of the same cartilage, supporting the interocular process of the frontal of the eye- 
less side. 
10, 10. 'The two orbitosphenoids, their cartilaginous tips pointing over towards the ocular side. 
Fig. 4. Anterior part of another cranium seen from above, but slightly tilted round towards the eyeless 
side. The frontal bones are removed, and two black bristles are passed, one through each 
olfactory foramen, as in fig. 3. 
Fig. 5. Same part of the cranium, but drawn from another specimen, seen from the ocular side, though 
slightly tilted round towards the eyeless one. A bristle is passed through the olfactory foramen 
of the eyeless side. : 
Fig. 6. The same, seen from the eyeless side. The lettering in this and the two preceding figures is ex- 
plained under figures 1, 2, 3, and 17. 
Fig. 7. The two frontal bones of the Turbot. 
11’, That of the ocular side: m’, its interocular process. 
11. That of the eyeless side: m, its interocular process; n, its external angular one. The position of 
the eyes is diagrammatically indicated in dotted outline. 
Fig. 8. Upper surface of the cranium of the Halibut (Hippoglossus vulgaris). The orbit is here on the 
right side, instead of on the left as in the Turbot. 
A. Cartilage of the nasal part of the cranium, as in the Turbot. 
9. A notch in the cartilage, into which a laminar projection from the interocular process (m/) of the 
frontal bone of the ocular side is received. 
h. A smaller notch in advance of the other, which receives a similar lamina developed on the end of 
the more slender interocular process (m) of the other frontal. 
pq. Two facets on the end of the vomer ; that of the eyeless side (p) is larger and looks more late- 
rally than the other (g). On these two facets move the heads of the corresponding superior 
maxillary bones, with the interposed fibro-cartilaginous disks. 
k. The prominence on the nasal bone on which the intermaxillary cartilage glides, and directed ob- 
liquely towards the eyeless side. Compare this with the corresponding part in the Turbot (fig. 1). 
Fig. 9. Under surface of the same cranium. Lettering as in the corresponding view of the Turbot’s 
cranium, 
Fig. 10. Anterior part of another cranium, seen from aboye, though slightly tilted towards the eyeless 
(left) side; the two frontals removed. A bristle passed through each olfactory foramen. 
gh. The two notches in the primordial cartilage, already referred to under fig. 8. The remaining 
lettering is the same as in the figures of the Turbot’s cranium. 
Fig. 11. The two frontal bones of the Halibut. Lettering as in figure 7. 
Fig. 12. Cranium of the Plaice (Platessa vulgaris), seen from above. Lettering as in the figure of the 
Halibut’s cranium (fig. 8). The prefrontal bone and olfactory foramen of the eyed side (right) 
are much in advance of the corresponding parts on the eyeless (left side); and the ridge (k) on 
which the intermaxillary cartilage glides is directed to the eyeless side at an angle of 45°. 
Fig. 13. Under surface of Same cranium. Lettering as before. 
