The Lateral Line System in Siluroids. 537 



ossification. Wliere the canal ceases to curve sharply the second pore 

 occurs and near it lies the first sense organ which is rudimentary. 

 The third pore is still some way in front of the level of the nose and 

 the second sense organ which lies midway between the two pores is 

 small. It lies in one of the smallscale - like bones. The 3rd sense 

 organ is at the level of the anterior part of the incompletely divided 

 nasal opening where the bones begin to be more continuous. The 4th 

 pore opens in front of and below the eye. The 4th sense organ is 

 at the anterior level of the orbit. Behind it occurred a slight ano- 

 maly in that before the 5th sense organ is reached two pores (5a and 

 5b) are seen below the orbit. The other side did not however show 

 this peculiarity. The 5th sense organ, 6th pore and 6th sense organ 

 follow in regular succession. The 7th pore is reached by a compara- 

 tively long branch which lies over the squamosal bone. The canal 

 curves upwards behind the eye at the edge of this bone and in the 

 postfrontal, which is small it unites with the supraorbital canal. No 

 sense organ and no pore is found near the junction and what is worthy 

 of notice the canal runs almost in a continuous line with the supra- 

 orbital. 



There are 6 sense organs and 7 pores in this system. 



Supraorbital system. The first two pores lie not far apart 

 in front of the nose and between them is the rudimentary first sense 

 organ. The second sense organ and 3rd pore lie laterally and internal 

 to the nose. The canal then curves outward and backward to the 

 level of the front of the orbit where the 3rd sense organ is situated. 

 Directly behind this and between the eyes a broad canal 

 passes across to join its fellow of the opposite side in 

 the frontal bones. The 4th sense organ lies in the frontal bone 

 at the level of the middle of the orbit and behind it a branch is 

 given off which passes medianly towards the junction 

 of the parietal and squamosal bones without however 

 passing beyond the frontal. The canal then curves outwards to join 

 the infraorbital in the postfrontal bone. 



The median branch contains a sense organ 5. 



There are 5 sense organs and 4 separate pores in this canal, 

 the median commissure starting between sense organs 3 and 4 taking 

 the place of a pore and no pore being formed at the junction with 

 the infraorbital canal. 



Main canal. This continues backwards in the postfrontal from 

 the junction of supra- and infraorbital systems. Near the suture ol' 



