306 ANATOMY OF VERTEBRATES. 



the large sac of the otolite, ib. i, 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. Its division on the acoustic sac is 

 shown, in the Perch, at s, s, fig. 203. 



The nervus vagus, ib. t, has a developement proportional to 

 the extent and complexity of the l^ranchial apparatus in Fishes, 

 and is usually larger than the trigeminal : it rises, fig. 185, 8, from 

 the restiform tract forming the side of the medulla oblongata, and 

 commonly from a sj^ecially developed lobe ; and is distributed to 

 the branchial apparatus, the pharynx and pharyngeal arches, the 

 ossophagus and stomach ; it sends filaments to the heart, and to 

 the air-bladder when this exists ; and it forms, or helps to form, 

 the ' nervus lateralis.' In the Lamprey a portion of the vagus 

 combines with branches of the facial and hypoglossal nerves to 

 form a short side-nerve extending to the middle third part of the 

 body. In Salmo, Clujoea, Acipenser, the 'nervus lateralis' is formed 

 exclusively by the vagus : in the latter, as in Chimcera, Balistes, 

 Diodon, Cydopterus, this nerve is a single longitudinal one : in 

 most bony fishes there are two which run parallel or nearly so. 

 In all these fishes it is continued very far back along the lateral 

 or latero-dorsal region of the body ; sometimes lodged deeply in 

 the lateral mass of muscles, e. g. Belonc, Clupca, and Scomber,^ 

 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 it has both 

 a deep-seated and a superficial branch. In Upeneus the super- 

 ficial Ijranch is sent off", dorsad, at an open angle from the main 

 trunk, to the lateral line, above which it runs in the Belone, the 

 superficial liranch descends to gain the lateral line. In the 

 Carp and Herring the vagal ' ramus lateralis ' sends ofl:' a strong 

 branch to the dorsal fin ; in the Garpike it sends, as in the Cod, 

 branches to tlie pectoral and ventral fins ; it distriljutes other 

 branches to the skin and mucous ducts; and some of these, in 

 most fishes, anastomose with branches of the spinal nerves, fig. 

 205. In the Perch there are two 'nervi laterales' on each side; 

 the dorsal one, fig. 203, m, above described, and the proper lateral 

 nerve, ib. I : this is formed exclusively by the vagus, and divides 

 into a superficial branch, supplying the lateral line, and a deep- 



' XX. vol. iii. p. 49, iircp. no. 1381 (mackerel). 



