MUSTELUS LJ]VIS. 109 



greater part of its course, directly superficial to the mandi- 

 bular part of the adductor inandibulEe muscle, near, and 

 nearly parallel to, its anterior edge. At its mesial end the 

 canal extends beyond the adductor muscle, and there lies 

 superficial to the cartilage of the mandible. The canal has 

 very closely the length and direction of the anterior edge of 

 the mandibular part of the adductor muscle. The canal does 

 not approacli any of the other canals, either anteriorly or 

 posteriorly, and the canals of opposite sides are separated at 

 their anterior ends by a considerable interval. 



The number of organs contained in the canal could not be 

 determined, neither the organs nor the nerves innervating 

 them being suflficiently developed to be traced with certainty. 

 There were twenty-two tubules along the line, counting the 

 anterior and posterior terminal ones. As most of these 

 tubules seemed to be primary ones that had not undergone 

 subdivision, there should be about twenty-one organs in the 

 line. 



'J'he organs are all innervated by branches of an anterior 

 or mandibular division of the mandibularis externus facialis, 

 a large branch of the nerve innervating also the mandibular 

 group of ampullae. 



Ampulla3 and Surface Sensory Organs. 



There are in Mustelus four groups of ampullae on each bide of 

 the head. These four groups correspond in general position 

 to the superficial ophthalmic, inner buccal, outer buccal, and 

 mandibular groups of Ewart's (18) descriptions of sela- 

 chians, but the group that has the position of an inner 

 buccal group is innervated by branches of the ramus oph- 

 thalmicus superficialis, instead of by branches of the buccalis 

 facialis, as will be fully described in describing the nerves. 

 The group in Mustelus is accordingly not the homologue of 

 the inner buccal group of Ewart's descriptions, and I shall 

 describe it as the deep ophthalmic group. No group corre- 

 sponding to Ewart's liyoid group was found, but it may, 

 perhaps, be represented by a line of surface organs. 



