MTJSTELUS L7RV1S. 119 



canal, at a beud in that canal. It then runs forward and 

 mesially, and, anastomosing with the corresponding canal 

 of the opposite side, forms a median longitudinal section 

 of canal which lies directly between the nasal apertures on 

 the dorsal surface of the anterior end of the snout. The 

 canal then turns laterally and backward, ventral to and 

 ai'ound the nasal aperture, and, posterior to the aperture, 

 anastomoses with the distal end of the snpra-orbital canal. 

 It then makes a double turn, first upward and then back- 

 ward, giving off the hyomandibular canal at the first bend, 

 and, having encircled the inferior and posterior edges of the 

 eye, reaches and anastomoses with the hind end of the supra- 

 orbital canal dorso-posterior to the eye. It then turns back- 

 ward, and reaches and anastomoses with the lateral end of 

 the supratemporal cross-commissure. Posterior to this 

 point it becomes the la.teral canal of the body. 



The supra-orbital canal begins between the eye and the 

 nasal aperture, there being in direct communication with the 

 infra-orbital canal, at a bend in that canal and at a point 

 that lies between two distinct groups of the oi-gans of the 

 line. The canal first runs forward and mesially on the top 

 of the snout, but, dorso-postero-mesial to the nasal aperture, 

 turns sharply backward, anastomosing at or near this bend 

 with the anterior end of the infra-oi'bital canal. It then 

 continues backward dorsal to the eye, until it reaches and 

 anastomoses with the infra-orbital canal between its otic and 

 postfrontal sections. 



If the canals of this imaginary or projected head of 

 Mustelus be compared with the canals of Amia, it will be 

 seen that that section of the infra-orbital canal of Mustelus 

 that contains the first group of organs of that line, Nos. 

 1 to 45, and that lies between the two anastomoses of the 

 infra-orbital canal with the supra-orbital one, corresponds, 

 in many respects, with that part of the infra-orbital canal 

 of Amia that encloses the first four infra-orbital organs of 

 that fish (2, p. 514). Those four infra-orbital oi'gans form, 

 in Amia, a distinct and separate group, and lie in a part 



VOL. 45, PART 2. — NEW SEKIKS, K 



