170 



As, however, in tlie single series of sections on wliicli fig. 

 23 was based it was innervated by the inner buccal of the 

 right side, it either cannot represent the anterior end of 

 the left supraorbital, or such an innervation must be 

 anomalous. In the meantime, however, we shall follow 

 Traquair, and regard it as belonging to the supraorbital 

 system. Another very small follicle was found behind it, 

 but it was very aborted and contained no sense organ. 

 The innervation of the former structure suggests that it is 

 a modified pit organ, especially as such occur typically in 

 Teleosts at this region. 



The Supraorbital commissure (s. o. c). — Arises from 

 the canal on the ocular side, as above described. A sense 

 organ is situated just at its origin, which projects partly 

 into the supraorbital canal itself. The commissure passes 

 upwards and forwards almost at right-angles in the sub- 

 stance of the right frontal. It then bends sharply inwards 

 at right angles (indicated by a circle in fig. 23), and at 

 once enters the left frontal. Just at the turn an unpaired 

 surface tubule (3) is given off, and this undoubtedly cor- 

 responds to the fourth unpaired median tubule of the Cod. 

 Its position in the Plaice is only apparently anomalous. 

 The commissure j^asses almost transversely but slightly 

 forwards across the body in the left frontal. Arrived at 

 the other side it bends gradually downwards but still for- 

 wards (a large sense organ being situated at the turn), and 

 thus passes into the left supraorbital. The sense organ in 

 the commissure on the left side is situated much higher 

 up than on the other side, and is thus entirely within the 

 commissure. It is innervated by the E.. ophthalmicus 

 superficialis vii. of the left side. The commissure also is 

 passing forwards from right to left during the whole of its 

 course. 



To sum up the supraorbital system, the right supra- 



