DR. TRAQUAIR ON THE ASYMMETRY OF THE PLEURONECTIDE. 295 
29, 30. Lower jaw, hollowed out to contain the eight ampullæ of the operculo-mandibular canal. 
8. Mastoid; and 11, left frontal: also hollowed, to support the ampullæ of the main canal. 
14. Left prefrontal. 
Fig. 8. Sketch of head and fore part of body of a monstrous specimen of Platessa flesus; the mucus- 
canals indicated in outline. 
Fig. 9. Anterior part of the same fish, but seen from the eyeless side; the mucus-canals also indicated 
in outline. The lettering in both this and the preceding figure corresponds to that in figures 
3 and 4. 
PLATE XXXII. 
Fig. 1. Diagrammatic view of the mucus-canals and superficial face-bones on the head of the common 
Cod (Gadus morrhua). 
aaaa. Mucus-canal of lateral line, extending along the top of the head, and ending in the turbinal 
ossicle (19), which is indicated in outline. 
b. Supratemporal canal; supratemporal bones (72) also in outline. 
c. Operculo-mandibular canal, which has no communication with the main canal in the Cod (Munro). 
d. Suborbital canal; 73’, suborbital bones. 
€. Cross commissure. 
Fig. 2. Diagram of the corresponding parts in the Turbot. 
a’, Left lateral canal. 
b'. Left supratemporal branch, with the supratemporal ossicles indicated in outline. 
€. Left operculo-mandibular branch. 
d'. Left suborbital canal and bones. 
e. Commissural branch. 
a. Right lateral canal, crossing the head beneath the dorsal fin (which is indicated by the line p F), and 
beneath both supratemporal canals, as it curves round between the eyes, side by side with its 
fellow of the left side. 
6. Right supratemporal canal and chain of bones. 
c. Right operculo-mandibular. 
d. Right suborbital canal and bones. 
19'. Left turbinal, and 19, right turbinal ossicle. 
LN F. Left nasal fossa. 
RNF. Right nasal fossa. 
DF. Line of dorsal fin. 
Fig. 3. Diagram of the corresponding structures in the Plaice. Here the eyes are placed upon the right 
side. 
a! a. Right lateral canal, extending between the eyes all the way to the nose, where it ends in a well- 
marked * turbinal ossicle.” 
f. Right supratemporal canal and range of ossicles. 
c. Right operculo-mandibular branch. 
d'. Right suborbital branch and chain of bones. : 
d*. Anterior suborbital bone of the right side, separate from the rest, and having no connexion with 
the mucus-canal. 
aa. Left lateral canal, apparently stopping short at the commissure (e). 
a*. A small detached portion of that canal, being in fact its nasal extremity. Owing to, or at least 
coincident with, the imperfect development of the interocular process of the n frontal in the 
Plaice, the part of the left mucus-canal which should extend between the eyes in that process 
has likewise not been developed. 
VOL. XXV. 2T 
