Nos. IAND2.] AXATOMY OF SCOMBER SCOMBER. iSi 



branches are said to pierce and traverse certain of the muscles 

 of the eyeball. In Salamandra the ramus nasalis is said by von 

 Plessen (No. 57) to lie dorsal to the opticus, and I have assumed 

 it to so lie in Necturus. This indicates, if I am right in my inter- 

 pretation of Herrick's statement, either some error in the descrip- 

 tions of this nerve, or some important difference to be explained. 

 In Ammocoetes, the supraorbital line of ganoids and teleosts 

 seems to be represented by a single organ said by Alcock (No. 

 I, p. 136) to be innervated by the so-called third facial nerve of 

 the fish. As the so-called ramus ophthalmicus superficialis of this 

 fish "runs forward between the eyeball and the floor of the orbit," 

 "and is concerned only with the innervation of sense organs be- 

 longing to the lateral line system," it would seem to be, unques- 

 tionably, the homologue of the buccalis facialis of ganoids and 

 teleosts. FiArbringer, however, says (No. 26, p. 62) that it lies, 

 in Petroniycon, dorsal to the nervus opticus and nervus oculomo- 

 torius ; and his figures seem to show it ventral to the nervus 

 trochlearis, that is in the position of a nervus profundus. What 

 the homologue is, in ganoids and teleosts, of the line of sense 

 organs it innervates is thus uncertain, though it would seem to 

 correspond' to that organ of the supraorbital line that is, in 

 Scomber, innervated by a branch of the buccalis facialis. 



3. Preoperculo-Mandibiilar Canal. 



The preoperculo-mandibular canal begins, anteriorly, at a single 

 pore that lies on the iatero-ventral surface of the mandible close 

 to its tip and not far from the corresponding pore of the same 

 canal of the opposite side of the head. From this point the canal 

 enters the dentary, and running backward through that bone 

 issues on its outer surface near the hind end of its ventral arm. 

 Here it lies for a short distance in an open groove on the outer 

 surface of the adjoining ends of the dentary and articular, then 

 enters the latter bone, and issues at its hind end immediately pos- 

 tero-ventral to the hind end of the articular surface for the quad- 

 rate. It then traverses the dermal tissues between the mandible 

 and preoperculum, lies, for a short distance, in an open groove 

 on the outer surface of the latter bone, which bone it then enters 

 and traverses its full length. Issuing at the dorsal end of the 



