169 



right nasal, on which it ends by a pore. It has only 3 

 pores and 4 sense organs, omitting those in the commis- 

 sure. It is curious to find that opposite the entry of the 

 commissure there is a small blind diverticulum, containing 

 no sense organs, and corresponding exactly to a similar 

 structure found in the Cod (see fig. 23).* 



The Left Supraorbital {sup. cJ). — Anastomoses with 

 the left infraorbital just as on the opposite side, passes 

 forwards within the left frontal for a short distance, and 

 receives the commissure. Just opposite the latter point 

 it gives off a surface pore below which may correspond to 

 the blind sac of the ocular side. Between its anastomosis 

 with the left infraorbital and reception of the commissure, 

 it has one large sense organf but no pore (cp. other side, 

 fig. 23). In front of the commissure the canal leaves the 

 frontal, but still lies in a depression on it, and ends 

 blindly a short distance anterior to the commissure. This 

 description enables us to compare the condition in the 

 Plaice with that of the Turbot, as described by Traquair, 

 and to correct the latter's figure of the Plaice in some 

 slight particulars. The other supposed remnant of the 

 left supraorbital canal, discovered by Traquair, is situated 

 far in front on the ocular side of the body very near the 

 dorsal edge and above but a little behind the anterior 

 extremity of the right supraorbital (figs. 23 and 29, 

 sup. c"). It consists of a very small follicle situated, 

 according to Traquair, on a minute ossicle representing a 

 greatly reduced left nasal, and containing two surface 

 pores, and, according to our sections, one sense organ. 



* Cole, Trans. Linn. Soc, ser. ii., vol. vii., pp. 157 and 180. 



t This sense organ, as well as the one on the left side of the supraorbital 

 conamissure, is innervated by the R. ophthalmicus superficialis vii. of the 

 left side. This is quite a conspicuous nerve, in spite of the abortion of 

 the greater part of its sensory canal. There can, therefore, be no question 

 that these parts of the canal system belong to the supraorbital canal. 



