THE ELASMOBRANCH FISHES 



245 



branches into a brancliio-intestinal bnndlo. The lateral line nerve can be traced 

 from the brain as a distinct stem. As it emerges from the cranium it swells out 

 into a large ganglion from which this branch proceeds posteriorly practically 

 to the end of the tail. From the lateral line ganglion there is given off a dorsal 

 root, the supratemporalis (fig. 245) which })asses upward and forward to 

 supply the suprateniporal canal, pit organs in the region of the supratemporal 

 canal, and the anterior part of the lateral line canal immediately behind the 

 segment supplied by the supratemporal branch of the ninth nerve. Posterior 

 to this branch there is given off a second branch, the dorsalis (d.X, fig. 220) 



Fig. 223. Brachial and pelvic plexuses, Eaja vomer. (From Braus.) 



which runs posteriorly almost to the first dorsal fin. This nerve supplies sense 

 organs of the anterior part of the lateral canal and also pit organs above the 

 line and anterior to the dorsal fin. Many branches are given off from the lateral 

 line nerve as it passes backward in the body to the sense organs along the 

 lateral line canal. 



The branchial stem in the vagus is a strong bundle which divides into four 

 (pentanchids), five (hexanchids), or six (heptanchids) branchial nerves. The 

 first two or three of these branchial nerves, except in Torpedo, where the first 

 and second branchials give off the third and fourth electric nerves, are essen- 

 tially like the branchial division of the glossopharyngeal. Each branchial con- 

 sists of pharyngeal and pre- and post-trematic nerves. The post-trematicus of 

 the vagus is composed of two strong branches, one of which is motor, the 

 other sensory. The motor division innervates the interarcual, interbranchial, 

 adductor, and ventral constrictor muscles. The last branchial nerve is com- 

 posed only of visceral sensory fibers (Norris and Hughes, 1920) . 



The ramus intestinalis or visceralis (vi.X) proceeds posteriorly after sepa- 

 rating from the branchial stem. Its motor fibers are distributed to the 

 trapezius muscle and to the digestive tract. Its sensory fibers go largely to the 

 digestive tract. 



The occipitospinales (y, z, fig. 220), back of the vagus, like spinal nerves 

 consist of dorsal and ventral roots, but dorsal roots to the ones most anterior 

 are frequently absent. In lowly forms, as we have seen in Heptanclius, several 

 pairs may be present. As many as five of the ventral occipitospinales have been 



