THE ELASMOBRANCH FISHES 241 



The oplithahiiicus profundus (op.V, fig. 220), after leaving its ganglion 

 passes forward deep in the orbit, between superior and inferior rectus muscles 

 and out anteriorly under the anterior rectus and between the obliques. On its 

 M^ay past the eyeball it gives off the ciliary nerves to the eye and then passes 

 to the dorsal and lateral parts of the snout (Squaliis), or also to the ventral 

 part (Mustelus). 



The ophthalmicus superficialis of the fifth (os.V, fig. 220) may have an ex- 

 tracranial ganglion as in Mustelus calif ornicus or it may be connected directly 

 with the gasserian ganglion as in Sqnalns acanthias. In either form the nerve 

 is closely associated with the superficial ophthalmic of the seventh on its way 

 through the orbit. In Squalus acanthias according to Norris and Hughes 

 (1920) there are three or four branches of this nerve which apparently ter- 

 minate in the skin over the supraorbital crest. In Mustelus calif ornicus the 

 nerve is larger and continues farther anteriorly. 



Both the ophthalmicus profundus and the ophthalmicus superficialis of the 

 fifth nerve are sensory. 



The maxillaris of the fifth {nix.Y, fig. 220) originates in the gasserian gan- 

 glion and passes to the jaw and on to the skin ventral to the snout. In its course 

 over the floor of the orbit it is accompanied by the buccalis of the seventh. 

 Near its ganglion it is often mediad of the buccalis but farther distally it may 

 lie dorsal to it. As a usual thing the maxillaris branches into two or three main 

 divisions, the most anterior of which passes forward almost to the tip of the 

 snout. 



The mandibularis may accompany the maxillaris over the floor of the orbit 

 and separate from it late to turn sharply back around the angle of the jaw as 

 in Laeniargus. Or, if the angle of the jaw is relatively far posterior, the 

 mandibularis may leave the maxillaris early and pass over the posterior wall 

 of the orbit to reach the angle of the mouth (Chlamydoselachus, Acanthias) . 

 In either form certain sensory bundles from the intracranial part of the gas- 

 serian ganglion, after passing the angle of the jaw, turn forward and supply 

 the skin of the lower jaw to the symphysis of the mandible. Motor fibers, dorsal 

 to the sensory fibers, supi^ly the levator maxillae, the first dorsal constrictor, 

 the adductor mandibulae, and a considerable part of the first ventral con- 

 strictor muscle (Norris and Hughes). 



The abducens or sixth cranial nerve is a motor nerve. It arises, as w^e have 

 seen, from a nucleus in the medulla and passes forward and outward to the 

 posterior rectus muscle, entering it at its base. 



The seventh or facial nerve like the fifth is composed both of motor and of 

 sensory components. Its motor fibers arise in the visceromotor nucleus (vm.n., 

 fig. 216) just posterior to that of the fifth nerve and extend to the lower jaw 

 and the facial region. Its sensory fibers are connected with large ganglia and 

 are distributed essentially as in Heptanchus. In Acanthias, the nerve may join 

 the brain in common with the branches of the eighth, and it is usually united 

 above with the fifth. In Mustelus canis, however, it may be more or less clearly 

 separate from the fifth (fig. 221). 



