282 DR. TRAQUAIR ON THE ASYMMETRY OF THE PLEURONECTIDÆ. 
1. The supra-temporal branch (b) at the back of the head, supported by the supra- 
temporal bones (7), indicated in the diagram in outline. 
2. The operculo-mandibular (c c), running in a groove, first in the preeopereulum and 
then along the lower jaw, where it ends near the symphysis. 
3. The suborbital (d), supported by the suborbital bones (7), running along beneath 
the eye, and terminating near the end of the snout, close to the end of the main canal, 
but to the outer side of the nostril. | 
The Arrangement in the Pleuronectide.—ln the genus Rhombus (Diagram, Plate 
XXXII. fig. 2), the lateral canal of the eyed side (a’ a’) pierces the suprascapular bone 
(»), then enters the first supratemporal bone, which bifurcates. The canal coming from 
the lower branch of the latter bone then enters the mastoid, passes from it to the frontal, 
and, arriving at the posterior margin of the orbit, gives off a branch (e) to communicate 
with the main canal of the opposite side. It then pursues its way in the stout inter- 
ocular process of the frontal, emerges from it at the anterior margin at the orbit, and 
ends, to the inner aspect of the nasal fossa of the ocular side, in a curved tubular ossiele 
(9), which we at once recognize as the ** turbinal." 
This eanal gives off, on its way, the following branches, as in the Cod :— 
1. The supratemporal (7^, issuing from the upper limb of the tubular bifurcated first 
supratemporal bone, proceeds, supported in a series of about sixteen little tubular ossicles 
constituting the rest of the supratemporal range, towards and along the base of the 
cephalie end of the dorsal fin, to beyond the middle of the upper eye, where it ends. 
These little bones have been indicated in the diagram by simple outline (72). 
2. The operculo-mandibular (c), given off while the main canal is still in the mastoid 
bone, runs in a tube hollowed out in the preopereulum and lower jaw-bones, and ends 
near the symphysis of the jaw. 
3. The suborbital branch (d^, given off opposite the origin of the commissural branch (e) 
already referred to, runs in a series of about nine minute tubular ossicles (7) under the 
lower eye, and ends, to the outer side of the nasal fossa of the ocular side, in an ossiele 
much larger than the rest, which is suspended to the prefrontal bone of the same side. 
The series of little ossicles is the suborbital range of bones ; the larger anterior one is ofa 
triangular shape, elongated, and with the apex directed posteriorly; on its surface is à 
tube which lodges the terminal portion of the mucus-canal. This terminal portion, 
however, seems to be isolated and distinct from the rest of the suborbital canal. 
On this side, the arrangement is very plain, the main canal curving round between the 
eyes, following the morphological mesial line, while the supratemporal branch proceeds 
forwards according to the apparent or pseudomesial line, along with the dorsal fin. 
On the eyeless side the lateral canal is similarly related to the suprascapular and first 
supratemporal bones, and to the mastoid. The supratemporal branch proceeds forw ards, 
with the dorsal fin, in the pseudomesial line; and the operculo-mandibular branch 15 
given off and pursues its course exactly as on the ocular side. But the main en 
ern Sntéród.the frontal bone, and arrived at the posterior margin of the orbit, it gives 
off a commissural branch to join that of the other side (e) already mentioned. lt the 
passes between the eyes, lodged in the slender interocular process of the corresponding 
