JIUSTELUS L.EVIS. 123 



and they are iuuervated by branches of two nerves that arise 

 separately and independently, but close together, from the 

 ganglion of the buccalis, close to the base of the nerve itself. 

 The most anterior branch innervates organs 79 to 82; the 

 other innervating organs 83 to 86. 



Organs 87 to 110 form the third group, and they are 

 separated, by their innervation, into four sub-groups, two of 

 which are postorbital in position, while the other two occupy 

 positions corresponding, in their topographical relations, the 

 one to the postfrontal part of the infra-orbital canal of Amia, 

 and the other to the otic and glossopharyngeal parts together, 

 of the main infra-orbital canal of the same fish. The post- 

 orbital organs of Mustelus include organs 87 to 96 ; the post- 

 frontal ones, organs 97 to 102 ; and the otic ones organs 103 

 to 110. The organs of the entire group are innervated by 

 three nerves that arise close together from a posterior pro- 

 longation of the buccalis ganglion, and that have already 

 been described. That branch of one of these three nerves 

 that innervates organs 103 to 110 is certainly the homologue 

 of the nerve described by me in Amia as the ramus oticus 

 facialis. What the exact homologues are, in Amia, of the 

 other nerves of Mustelus that are here concerned is not easy 

 to tell. The nerve that, in Mustelus, innervates organs 97 to 

 102 would seem to be the exact homologue of the nerve that, 

 in Amia, innervates the single postfrontal organ. No. 14 inf., 

 of that fish. The nerve that innervates this latter organ in 

 Amia always arises close to the base of the ramus oticus, if 

 not from the base itself of that nerve, and in one specimen of 

 Amia I found it arising as a branch of the oticus after that 

 nerve had issued from its cranial canal on to the roof of the 

 skull (2, p. 515). But it is a branch of the oticus, in Amia, 

 that innervates the spiracular organ, while, in Mustelus, it is 

 a branch of the nerve that innervates organs 87 to 91. It 

 may then be that the three nerves of Mustelus that together 

 innervate organs 87 to 110 and the spiracular organ are the 

 homologue of the otic nerve of Amia plus that branch of the 

 buccalis that innervates the postfrontal organ No. 14 infra- 



