MUSTELUS L^VIS. 115 



orbital bend in the canal and the point where the hjoman- 

 dibular canal is given o&, the pores being most numerous 

 near the canal, and diminishing irregularly in number from 

 there backward. The long tubules run at first directly back- 

 ward, all having a nearly parallel course, the longest ones 

 extending beyond the level of the hind edge of the eye, and 

 therCj toward their hind ends, turning upward and backward. 

 Their external openings form a regular, curved, and well- 

 marked line which extends from the hind edge of the infra- 

 orbital canal, immediately below the spiracle, at first back- 

 ward and but slightly downward, then, having nearly reached 

 the level of the hind end of the hyomandibular canal, turns 

 downward and slightly forward, anterior to the hind end of 

 the latter canal, and ends near the ventro-lateral edge of the 

 head. There were forty-six pores in the sub-group. 



The tubules of the fifth sub-group form a continuation, on 

 the ventral surface of the head, of the broad band formed 

 by the fourth sub-group. Their external openings form a 

 long curved line, which begins on a level with, and consider- 

 ably lateral to, the hind edge of the gape of the mouth, and 

 from there runs backward and laterally, on the ventral sur- 

 face of the head, in a line lying mesial to and somewhat 

 parallel to the hyomandibular canal. There were twenty- 

 seven pores in the sub-group. 



The sensory organs of the entire group are all innervated 

 by two branches of the buccalis facialis in a manner that will 

 be fully described in describing that nerve. The innervation 

 of these ampullae by two branches of the buccalis may perhaps 

 indicate that they represent the united inner and outer buccal 

 groups of Ewart's descriptions of other selachians. 



The mandibular group of ampullag is a small one lying 

 slightly posterior to the lateral third of the mouth opening, 

 between it and the mandibular canal. In my 12"2 cm. speci- 

 men these ampullas were still in an undeveloped condition. 

 They had already sunk beneath the ectoderm and were united 

 in a close group, but none of them had as yet acquired the 

 pocketed form characteristic of the ampullae in all the other 



