244 



THE ELASMOBRANCH FISHES 



from a ganglion located on the nerve in or just outside the glossopharyngeal 

 canal (see fig. 220). The main divisions of the nerve are a branch {st.IX, fig. 

 220) to the anterior segment of the lateral line canal, and nerves in relation 

 to the first and second demibranchs. 



The supratemporalis (st.IX) in Squalus acanthias, according to Norris and 

 Hughes, supplies three neuromasts of the lateral line canal located between 

 the neuromasts supplied by the supratemporalis of the vagus and the ramus 

 oticus VII, but it is not provided with other branches to pit organs. In Chlamy- 

 doselachus, Ilawkes (1906) mentioned, in addition to the twigs to the neuro- 



A B 



Fig. 222. Brachial and cervical plexuses. A. Scyllium. B. Squatina. (From Max Fiirbringer.) 

 hr.p., brachial plexus; cr.p., cervical plexus; d.r., dorsal root; 0., occipitospinal nerve. 



masts of the lateral line canal, other twigs to the skin. These she suggested 

 were cutaneous. They possibly supply pit organs. In Raja radiata according to 

 Norris and Hughes there are no lateral line elements in the ninth nerve. 



Above the first branchial pocket, as in Heptanchus, the main part of the 

 ninth nerve, as the first branchial nerve, separates into three divisions, a pre- 

 trematicus {pr.t.), a post-trematicus (po.t.), and from the pretrematicus a 

 pharyngeal division (ph.IX), the last-named branch being sensory and com- 

 parable to the palatine division of the facial nerve. The pretrematicus is also 

 sensory; it extends do^\^l the hyoidean demibranch back of the branchial carti- 

 lages, supplying the mucous membrane and gill filaments. Unlike Heptanchus 

 the majority of Elasmobranchs seem to lack the internal pretrematicus. The 

 post-trematicus or larger division, unlike that of Heptanchus, is not always so 

 clearl}^ separated into its components. The post-trematicus supplies the mu- 

 cous lining along the anterior part of the first holobranch and other sensory 

 fibers continue forward under the gill cleft and are distributed to the mucous 

 membrane of the pharynx and buccal cavity. The motor branches supply 

 muscles associated with the first holobranch. 



Accompanying the glossopharyngeal and a part of it, in Torpedo, is the 

 second electric nerve. 



The vagus is the most widely distributed of any of the nerves. It is much 

 like the ninth in its supply of the gills, but in addition it gives off a dis- 

 tinct lateral line nerve, and its branchial divisions are bound with intestinal 



