196 LECTURE VIII. 



the glosso-phaiyngeal ; and says, " this nerve, on being touched 

 near its origin in a recently dead animal, immediately produces a 

 contraction of the muscular appendages of the gills." (ib. p. 41.) In 

 the Cod the acoustic nerve (fig. 53. 7), which here, as in all fishes 

 above the Dermopteri, is of large size, rises close behind, but distinct 

 from the fifth pair, between it and the vagus : the acoustic nerve 

 receives a filament from the vagus, extends in a crescentic form upon 

 the labyrinth, expands upon the large sac of the otolite, and sends 

 filaments to the ampulliform ends of the semicircular canals. In other 

 Osseous Fishes (Pike, Blenny), the acoustic blends at its origin with 

 the back part of that of the fifth : it sometimes communicates with 

 the opercular branch of the fifth as well as with the glosso-pharyngeal 

 of the vagus. 



The nervus vagus has a development proportional to the extent 

 and complexity of the branchial apparatus in Fishes, and is usually 

 larger than the trigeminal ; it rises (fig. 53. 55. 8) from the restiform 

 tract forming the side of the medulla oblongata, and commonly from 

 a specially developed lobe ; and is distributed to the branchial ap- 

 paratus, the pharynx and pharyngeal arches, the oesophagus and 

 stomach ; it sends also filaments to the heart, and to the air bladder 

 when this exists {Jig. 58. t). In the Lamprey a portion of the vagus 

 combines with branches of the facial and hypoglossal nerves to form 

 a ramus lateralis vagi, which extends to the middle third part of the 

 body, where it terminates. In the Cod we saw that the ' lateral nerve' 

 was formed chiefly by the trigeminal ; but in many Osseous Fishes 

 ( Cyprinus, Belone, and Coitus) the proportions are reversed, and the 

 lateral nerve is formed by a branch of the vagus, which receives 

 filaments from the trigeminal nerve : in a few genera ( Salmo, Cliipea, 

 Acipenser) it is formed exclusively by the vagus. In all these fishes 

 it is continued very far back along the lateral or dorso-lateral region 

 of the body ; sometimes lodged deeply in the lateral mass of muscles, 

 ex. gr. Belone, Clupea, and Scomber (Prep. 1384 of the Mackerel): 

 but more commonly the nerve or a main branch lies just under the 

 skin, and in the course of the lateral mucous line, as in the Salmon, 

 and Sturgeon : in the Flat fish and Bull-heads ( Cottus) it has both a 

 deep-seated and a superficial branch. In the Carp and Herring the 

 vagal 'ramus latei'alis' sends off a strong branch to the dorsal fin : in 

 the Gar-pike it sends, as in the Cod, large branches to the pectoral 

 and ventral fins : it distributes its smaller branches to the skin and 

 mucous ducts ; and those in the Cod and Lump-fish anastomose with 

 branches of the spinal nerves. In the Perch there are two ' nervi 

 laterales ' on each side ; the dorsal one, which escapes through the 



