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 vagits, ib. t, has a developement proportional to 



the extent and complexity of the branchial 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 specially developed lobe ; and is distributed to I 



the branchial apparatus, the pharynx and pharyngeal arches, the ) 



oesophagus 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 r 



combines with branches of the facial and hypoglossal nerves to i 



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



body. In Salmo, Clupea, Acipcnser, the 'nervus lateralis' is formed { 



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



Diodun, Cyclopterus, this nerve is a single longitudinal one : in 1 



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



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. Belone, Clupea, and Scomber, 1 



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 I 



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



ficial branch is sent off, dorsad, at an open angle from the main i 



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



superficial branch descends to gain the lateral line. In the 



Carp and Herring the vagal ' ramus lateralis ' sends off a strong 



branch to the dorsal fin ; in the Garpike it sends, as in the Cod, 4 



branches to the pectoral and ventral fins ; it distributes othei ] 



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. /: this is formed exclusively by the vagus, and divides 



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



1 xs. vol. iii. p. 49, prep. no. 1384 (mackerel). 





