The Latero-Sensory Canals and Related Bones in Fishes. 427 



dermal bone, the fifth one of these little bones occupying a position 

 corresponding to that of the postfrontal ossicle in Ameiiirus and Silurus. 

 The 6th. organ of the line is said to lie "at the level of the broadest 

 part of the skull", and it is shown, in Pollard's figure, in that part 

 of the canal that lies immediately anterior to the point of anasto- 

 mosis with the preopercular canal. It is said to be innervated by the 

 ramus oticus, and it is the only organ said to be innervated by that 

 nerve. Nothing whatever is said as to its being enclosed in bone, or 

 not. The 7 th., 8 th. and 9 th. organs are said to all lie in the 

 squamosal, the 7 th. organ being innervated by a branch of the glosso- 

 pharyngeus, and the 8 th. and 9 th. organs by branches of the vagus. 

 The 9 th. organ is said to be the last one belonging to the head. It 

 is evident from this description and by comparison with other silu- 

 roids, that the 6 th. organ must lie in the squamosal, notwithstanding 

 that it is not so stated. And it is also evident that the 8th. and 

 9 th. organs are respectively the extrascapular and suprascapular 

 organs of the fish, the related latero - sensory ossicles here both, if 

 Pollard is correct, being fused with the hind end of the squamosal. 



This fish thus apparently agrees strictly with Silurus glanis, ex- 

 cepting in that the suprascapular ossicle, as well as the extrascapular 

 one, is hei-e fused with the hind end of the squamosal. 



Chaetostomus. In a 3 cm specimen of this fish, Pollard [60] finds 

 five sense organs in the supraorbital canal, the posterior three of 

 which ai'e, according to his figure, enclosed in the frontal, though, in 

 the text, nothing is said as to the bone that encloses the 3rd. organ. 

 There is also nothing said as to the bones that enclose the 1st. and 

 2nd. organs of the line, and it is possible that, in his specimen, bone 

 had not yet here begun to develop. The 2nd. organ and the 3rd. 

 pore are both said to "lie laterally and internal to the nose", doubt- 

 less a typographical error, for both pore and organ are shown in the 

 figure lying mesial to the nose. The canal anastomoses by its 5th. 

 or penultimate tube with the main infraorbital. 



The first six organs of the main infraorbital line are antorbital 

 and circumorbital in position, as in Ameiurus, but the 1st. and 2nd. 

 organs only, are said to have a related protecting scale. The 6 th. 



