382 FISHES CHAP. 



each of which may have a ganglion on its root: (1) an 

 oplitlialmicus superficialis ; (2) a biiccalis nerve with its ramus 

 oticus ; and (3) external mandibular nerves which course in the 

 ramus hyomandibularis. The addition of the great lateralis 

 nerve, which is usually described as the lateral branch of the 

 tenth nerve, and of the eighth or auditory nerve which supplies 

 the auditory organ, completes the enumeration of the main 

 factors of the lateralis system. The ninth or glosso-pharyngeal 

 nerve, perhaps the -most typical of all the branchial nerves, 

 has pre- and post -branchial branches which enclose the hyo- 

 branchial cleft. Its palatine nerve usually extends forwards 

 and anastomoses with the corresponding branch of the seventh, 

 thus forming a connexion (Jacobsons anastomosis') between the 

 two cranial nerves. In some Elasmobranchs and Teleosts fibres 

 derived from the dorsal branch of the ninth nerve innervate a 

 few sense-organs of the lateral sensory canal of the head, and 

 hence that nerve sometimes contains lateralis fibres. The tenth 

 or vagus is a compound nerve. Besides the great lateralis nerve 

 generally associated with it, the vagus includes as many 

 typical branchial nerves as there are branchial clefts behind the 

 hyo-branchial cleft, and in Elasmobranchs and in Chimaera these 

 nerves have independent origins from the medulla oblongata. 

 Each nerve has the typical structure, a ganglionated trunk which 

 forks over a gill-cleft into the usual pre- and post-branchial 

 branches, and palatine branches to the pharyngeal walls. In 

 the Dipnoi the lateralis nerve is connected with the superficial 

 ophthalmic branch of the seventh nerve by a commisural nerve 

 which curves across the outer face of the auditory capsule. A 

 somewhat similar anastomosis is also present in Petromyzon. The 

 vagus also includes a large ramus intestinalis, which in Elasmo- 

 branchs, at all events, has a distinct ganglionated root. The 

 nerve forms characteristic plexuses on the oesophagus and stomach, 

 and in Cyclos tomes its branches may extend nearly the whole length 

 of the intestine. In Ganoids and Teleosts there is an interesting 

 nerve known as the " lateralis accessorius." It is a compound 

 nerve, and owes its formation to the union of somatic sensory 

 fibres derived in succession from dorsal branches of the v., vii., 

 ix., and x. nerves, and also from the corresponding branches 

 of a variable number of spinal nerves. The finer branches of the 

 nerve are distributed to the skin of one or more of the fins, or 



