296 DR. TRAQUAIR ON THE ASYMMETRY OF THE PLEURONECTIDÆ,. 
b. Left supratemporal canal. 
c. Left operculo-mandibular canal. 
d. Left suborbital branch and range of bones. 
e. Commissure. 
pr. Line of dorsal fin. 
RNF. Right nasal fossa. 
LN F. Left nasal fossa. 
Fig. 4. Diagram of the top of the head in the Plaice, showing the manner in which the orbit is formed. 
The dotted line, p F, indicates the morphological middle line; the other dotted line, r n, shows 
the direction of the dorsal fin. The shaded parts are those parts of the original and symmetri- 
cal plan of the head which have become developed; the parts of the same plan which have 
not become developed are indicated in dotted outline, while the parts in entire outline are 
additional developments. 
11’. Right frontal, with its interocular process (m). 
11. Left frontal, its interocular process atrophied, while a new process (n) has sprung from its external 
anterior angle. 
14. Right prefrontal, sending back a process (a) to articulate with the interocular part (m) of the right 
frontal. 
14. Left prefrontal — the part a, in dotted outline, and corresponding to the process (a’) of the bone of 
the other side, not having been developed, while a new process ( f), not found on the right pre- 
frontal, is sent back to articulate with the process (n) of the left frontal. By the union of the 
process (f) ofthe left prefrontal and the process (2) of the corresponding frontal, the * pseudo- 
mesial” bar of the cranium is formed, and the orbit bounded on the left side. 
15. Nasal bone; the unshaded part indicates a development from its left side, which enters into the 
anterior boundary of the orbit, apparently pushing aside the left prefrontal. 
€ c. Olfactory foramina. 
RE. Right eye. 
L E. Left eye. 
Fig. 5. Posterior surface f cranium of the Plaice. The dotted line, m p, shows the curve of the mesial 
line in this region, the convexity being towards the ocular or right side. 
Fig. 6. First vertebra ofthe Plaice, seen from the front, showing how its mesial vertical plane is convex 
towards the right or ocular side. 
Fig. 7. Seventh abdominal vertebra of the Plaice, seen from before, showing the more vertical direction 
downwards of the left transverse process. 
Fig. 8. Abdominal vertebræ of the Plaice, seen from below, and showing the unsymmetrical obliquity of 
the transverse processes from the fifth to the twelfth inclusive. 
Fig. 9. Anterior part of an embryo Flounder, magnified five times, showing the upper eye not yet fully 
turned round, and the dorsal fin not so far advanced on the head as we find it in the adult. 
The dorsal fin-rays are a little injured a little behind the head; but about the ocular region 
there is not the slightest trace of abrasion to be seen, so that there is no reason at all to suppose 
that {here any rays have been removed by violence. 
4. Line showing the natural size of the figured portion of the specimen. 
— M — MU eMMA———————————— nn 
