MUSTELUS Li^iVlS. 113 



tubules form a sub-group somewhat distinct from the 

 others. 



Those pores of this group that lie on the ventral surface of 

 the snout all lie anterior or mesial to the nasal aperture, and 

 there is a line of them on each side of the subrostral section 

 of the supra-orbital canal, and on each side of the prenasal 

 section of the infra-orbital canal, certain of the tubules here 

 crossing the lines of each of the two lateral canals, interual 

 to them, to reach their opposite sides. The pores that are 

 thus arranged in line on either side of the two canals are, iu 

 certain places, placed markedly one between each two 

 successive primary tubules of the related canal, canal tubules 

 and ampulla ry pores thus alternating. Certain of the 

 ampuUary tubules extend backward into the tissues that 

 cover the cartilages that lie iu the ventral wall of the nasal 

 sac, and in sections, but not in the dissections, certain of 

 them even had their openings in the very edge of the nasal 

 aperture. The tubules that reach the dorso-lateral surface 

 of the snout turn backward, and the related pores form a 

 band that extends backward to the anterior edge of that part 

 of the infra-orbital canal that bends forward below the eye. 

 There were in this entire group of ampullae, on the one side 

 of the head on which they Avere counted, 194 pores. The 

 ampullee are all innervated by branches of the ramus 

 ophthalmicus superficialis, as will be fully described iu 

 describing that nerve. 



The buccal group of ampullas lies ventral to the anterior 

 edge of the eye, in the region internal to that section of the 

 infra-orbital canal that lies between the suborbital bend in 

 the canal and the point where the hyomandibular canal is 

 given olf. The tubules of the group may be separated into 

 five sub-groups. The tubules of one of these five groups run 

 at first forward and upward, then curve gradually forward 

 mesially and downward, and have their external openings on 

 the dorso-lateral surface of the snout, lateral to the rostral 

 part of the supra-orbital lateral canal, between that canal 

 and the pores of that sub-group of the deep ophthalmic 



