478 AUGUSTA LAMONT ON 



The canals opening on the ventral surface are directed towards the tip of the 

 snout, and are arranged in a single group, sometimes with a few detached scattered 

 canals appearing scarcely to form a part of the group nor yet a group by themselves 

 (Plate II). 



(2) Inner Buccal Canals, 



These canals open on the ventral surface only, and are distributed in two groups, 

 one of which is directed backwards on the naso-buccal flap, while the other takes an out- 

 ward course in front of the nasal aperture, round which it then curves in a backward 

 direction (Plate IV, fig. 6). 



(3) Outer 1 Buccal Canals. 



The canals from the outer buccal ampullae opening on the dorsal surface are 

 comprised in a single small group situated a short distance anterior and exterior to 

 the front angle of the eye. They are few in number — in some cases not more than 

 seven or eight — and are directed from within outwards, so that they are readily 

 overlooked, and even when searched for are only distinguished with some difficulty. 

 They come to the surface immediately anterior to the mandibular muscle, and just 

 on the outer side of the infra-orbital (sensory) canal, from the branches of which 

 they can be distinguished by their soft consistency and hyaline appearance, which 

 contrast with the tougher texture and opaque white appearance of the sensory canals, 

 characters which also combine to give the respective openings of the two systems 

 a different appearance. These canals appear to have been overlooked by previous 

 investigators ; like the dorsal canals of the ophthalmic ampullae, they go unrecorded 

 by Sappey, who gave more attention than others to the distribution of the ampul- 

 lary canals, and they are not represented by Garman in his figure of Raia Isevis 

 mentioned above (Plate I). 



Three groups of canals open on the ventral surface : — (l) An outer group has 

 typically — but subject to modification in some species — an arrangement in which 

 the canals diverge forwards, outwards, and backwards in radiating fashion, over- 

 lapping the most anterior canals of the hyoid ampullae. (2) An anterior group is 

 composed of canals directed forwards. (3) A posterior group lies external to the 

 naso-buccal groove, and its canals are directed backwards (Plate II). 



Collectively the canals of the ophthalmic, inner buccal, and outer buccal ampullae 

 opening on the ventral surface occupy the region between the tip of the snout, the 

 mouth, and the propterygium. The openings appear to be irregularly scattered, 

 and even after removal of the skin it is not always easy to say from which group of 

 ampullae the canals arise, and they must be traced back and the ampullae exposed 

 before this can be decided. As the ampullae are deeply situated, and as the canals 

 are short, the course of these is directed largely from within outwards rather than 

 along the surface, and they appear as little tufts radiating from within towards the 

 exterior. Except in cases where pigment is present in the canal-walls, they are so 



