3 S2 FISHES CHAP. 
each of which may have a ganglion on its root: (1) an 
ophthalmicus superficialis ; (2) a buccalis nerve with its ramus 
oticus ; and (3) external mandibular nerves which course in the 
ramus hyomandibularis. The addition of the great Jateralis 
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 (Jacobson’s 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 origims 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 ganghonated root. The 
nerve forms characteristic plexuses on the oesophagus and stomach, 
and in Cyclostomes 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 1s 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 
ath ewe 
