242 



THE ELASMOBRANCH FISHES 



For convenience of description we may consider the facial nerve as made up 

 of two groups of fibers. One of these supplies the sensory canal system; the 

 other belongs to the facial i)roper. Three great nerves are in the service of the 

 sensory canal system. These are : the ophthalmicus superficialis {os.YII, figs. 

 220 and 221) which goes to the supraorbital canal and associated ampullae of 

 Lorenzini; the buccalis, to the infraorbital canal and associated ampullae of 

 Lorenzini; and the external mandibular, a branch of the hyomandibular 

 nerve. This supplies the hyomandibular and the mandibular canals (figs. 220 



and 245), and ampullae 

 of Lorenzini. 



The ophthalmicus su- 

 perficialis of the facial 

 {os.YII) is a somewhat 

 large nerve which arises 

 from a large ganglion 

 (figs. 220 and 221) and 

 runs forward into the or- 

 bit. Generally it enters 

 the orbit through the or- 

 bital fissure in common 

 with the trigeminal, but 

 in certain types (Mus- 

 i elus henlei) it may enter 

 through its o^\^i foramen 

 above and in front of 

 the orbital fissure. As it 

 passes through the orbit 

 superficially, it gives off 

 numerous branches dorsally to the supraorbital canal and associated ampul- 

 lae and leaves the orbit by a large anterodorsal foramen. It extends forward 

 giving off a large branch which passes downward in front of the eye to supply 

 the lower part of the supraorbital canal and numerous small branches which 

 pass toward the tip of nose. 



The buccalis may arise from a large ganglion which is continuous with that 

 of the ophthalmicus superficialis VII {Acanthias, fig. 220, hu.VII). In Mus- 

 telus calif ornic us these two ganglia are distinct but the ganglion of the buc- 

 calis is in close relation to the ganglion of the external mandibular nerve. The 

 buccalis, as was previously mentioned, runs across the floor of the orbit closely 

 associated with the maxillaris of the fifth. In the anteroventral angle of the 

 orbit it divides into two or three main divisions, the twigs of which go to sup- 

 ply the infraorbital canal and associated ampullae of Lorenzini. From the 

 ganglion the buccalis sends off branches which supply the part of the infra- 

 orbital canal posterior to the eye (see p. 279, fig. 245) , and from the dorsalmost 

 part of the ganglion it gives the important ramus oticus VII to a short seg- 

 ment of the most anterior part of the lateral line canal. 



Fig. 221. Eoots of fifth and seventh nerves, Mustelus canis. 

 (From Green.) 



hu.VII, buccalis of seventh; ct., chorda tympani; g., 

 geniculate ganglion; 7(7nd., hyomandibular nerve; mx.md.V . 

 maxillaris and mandibularis of fifth ; F777, auditory nerve ; 

 op.V, ophthalmicus profundus; os.V, ophthalmicus super- 

 ficialis of fifth; os.V II, ophthalmicus superficialis of the 

 seventh; pl.VII, palatinus of seventh; prt., pretrematicus ; 

 sp., spiracle. 



