THE ELASMOBRANCH FISHES 225 



which run two main branches; the anterior branch passes outward and divides 

 into two divisions; the other passes backward and separates into numerous 

 twigs. Tliis nerve supplies the ampullae of the semicircular canals and sends 

 divisions to other parts of the ear. 



The glossopharyngeal or ninth nerve (IX, figs. 200a and 203) arises back 

 of the sixth and farther from the middle line and passes posteriorly under 

 the floor of the auditory capsule. Before reaching the surface it gives off a 

 branch (st.IX, fig. 203) from which sui)ratemporal branches are sent off pre- 

 sumably to the anterior segment of the lateral line canal. Another branch 

 [dr. IX) passes upward and backward from the supratemporal but its desti- 

 nation has not been determined. After leaving the cranium the glossopharyn- 

 geal bears a ganglion ign.) dorsal to the first branchial cleft, from which pro- 

 ceeds the main pretrematicus nerve ipri.) ; this nerve runs down the hyoidean 

 demibranch in front of the first gill pocket. A pharyngeal branch (ph. IX) 

 arises from the ganglion over the dorsal angle of the first cleft and passes for- 

 ward to supply the dorsal pharyngeal wall. From the pharyngeal in Hep- 

 tanchus macula t us there is given off an internal pretrematic (prt.i.). The 

 third division of the nerve is the post-trematicus (po.t.) which passes back 

 of the first cleft, in the anterior demibranch of the first whole gill. In Hep- 

 tanchus maculatus the post-trematicus is divided into two distinct bundles, 

 of which the anterior is sensory and the posterior is mixed. The posterior 

 branch of the post-trematicus continues to the ventral pharyngeal region, 

 supplying motor branches to muscles and sensory fibers to the mucous mem- 

 brane. One of its sensory branches curves forward and runs dorsally past the 

 end of the anterior sensory root. 



The vagus or tenth cranial nerve {X, figs. 200a and 200b) leaves the brain 

 stem by a number of roots. Some of these roots arise ventrally close to the 

 origin of the ninth. Others arise in a crescentic line from this almost to the 

 middorsal line. The nerve leaves the cranium through a large foramen and 

 outside appears in three main divisions. One of these, the lateralis nerve {ll.X, 

 fig. 203), supplies the lateral line and extends practically to the tip of the 

 tail. The branchial divisions ( 6 r.X^"*^ ), consisting of six nerves, pass backward 

 and then ventrally to supply the gill area not supplied by the glossopharyn- 

 geal; while the third division, the visceral (6/.X), passes on to the viscera. 



The lateralis nerve (ll.X) is the most anterior bundle of the vagus arising 

 from the brain (figs. 200a and 200b). It continues backward more or less 

 separate and distinct even in the canal where it gives off two branches, one of 

 which (st.X, fig. 203) passes to the supratemporal and lateral sensory canals, 

 the other (dr.X) being distributed to the area of the pit organs along the back. 

 The lateralis then runs along the wall of the anterior cardinal sinus and 

 finally passes posteriorly between the dorsal and lateral bundles giving off 

 branches to the lateral line. 



The branchial nerves to the gills (hr.X^~^) lie in the floor of the anterior 

 cardinal sinus. Distal to their ganglia each of these nerves comprises the same 

 number of parts as the ninth, pretrematicus, post-trematicus, and pharyngeal 



