536 H. B. POLLARD, 



the nose. The second sense organ lies exactly at the level of the centre 

 of the eye in the frontal bone. The 4th pore occurs slightly more 

 posteriorly and beyond it the canal curves outwards to join the infra- 

 orbital at the large pore behind the eye. The 3rd sense organ lies 

 midway between the pores. 



There are in the supraorbital system 3 sense organs and 5 pores, 

 four of the latter being really half pores. 



Main canal. The main canal is continued backwards from the 

 junction of the supra- and infraorbital systems. Sense organ 3 occurs 

 in what is probably the postfrontal bone, though the latter becomes 

 intimately applied to cartilage, above the articulation of the hyoman- 

 dibular. Pore 5, sense organ 4 and pore 6 follow at regular intervals 

 the canal taking a straight course backwards. The 5th sense organ 

 is situated not far from the 6th pore. Beyond it the canal which 

 lies here in the "suprascapular" bone becomes markedly increased in 

 calibre. At this part of its course it is not bounded internally imme- 

 diately by bone but faces a large space in which lies the structure 

 which has been called the swim bladder and which communicates with 

 the sacculus of the ear. 



The canal continues as the body line backwards. There is no 

 operculo-mandibular canal at this stage. 



Innervation. The two organs of the infraorbital system are 

 supplied by two twigs representing the buccalis. The first runs clo- 

 sely apposed to the maxillaris superior. The supraorbital organs are 

 supplied by the ophthalmicus superficialis the first receiving its nerve 

 from the median side. Sense organ 3 in the main line is supplied by 

 the Ramus oticus, 4 by the Glossopharyngeal and 5 by the first branch 

 of the Vagus. A supratemporal branch could not be detected running 

 into the recurrens facialis. This latter nerve gives off remarkably 

 far forward the large nerve which proceeds to the pectoral fin which 

 in this case has unmistakeably no connection with the first spinal 

 ganglion. 



Chaetostomus (juairensis, (Fig. 6.) 



Young specimen, 3 cm in length. 



Suborbital canal. This has a very long course at the side 

 of the snout. It commences far forward and the first pore is quite 

 laterally placed. The canal curves upwards and backwards, enclosed 

 in a thin tube of bone the skin in this region possessing no other 



