46 CLASS XIV. 



lateralis cannot be a nerve of motion*; its branches, even when it is 

 situated more deeply, go to the skin. 



The sympathetic nerve is not present in the Cyclostomes, its 

 place being supplied apparently by the w. vagus. In the Plagio- 

 stomes the cephalic portion is wanting ; in the bony fishes this por- 

 tion is situated on the outside of the cranium between the nervus 

 trigeminus, glossopharyngeus and vagus on each side, where it 

 forms three ganglia situated behind one another, which are con- 

 nected by a string running longitudinally, a continuation of the 

 sympathetic nerve of the trunk. Mostly the two sympathetic 

 nerves are united by a transverse branch beneath the bodies of the 

 anterior vertebra3. There are two nervi splancloiici, usually one on 

 each side ; in different fishes the two arise from one ganglion on the 

 right side, and are then only very rarely united at their origin into 

 one stem^ 



The sense of touch is little developed in fishes. Proper organs of 

 tact, like our fingers, by which the form of objects may be investi- 

 gated, are wanting, although the lips perhaps may partly serve for 

 tact. Often there are soft conical appendages or filaments at the 

 lips or jaws which, like the whiskers of mammals, serve for the 

 investigation of external obstacles, and put fishes in a condition 

 to avoid them. The entire skin is little adapted to convey a fine 

 sense of touch ; it is the seat of a mucous secretion often largely 

 developed, and is usually covered with scales (see above p. 11). 

 The scales present many stria? parallel to the edge, and thus appear 

 to be formed, like the shells of bivalve molluscs, of superposed 

 laminae, as Leeuwenhoeck supposed. Later observers, however, 

 have opposed this laminated origin of scales as horny plates. The 

 scales are not situated in the epidermis alone, but really in the skin, 

 and are included by it ; on a fibrous layer formed of connective 

 tissue there lies a layer of pigment, which is covered by an epidermis 



^ As little is the ramus lateralis n. trigemini, less usual in fishes, a motor nerve ; it 

 arises as a branch which mounts upwards to the cranium, mostly joined by a branch 

 from the n. vagus, and afterwards continues its course along the whole of the back 

 (beneath the dorsal fin). This nerve receives a small branch from all the spinal 

 nerves. 



^ Compare on the nervus sym2Mihiciis of fishes E. H. Weber Anatomia compar. 

 nem sympalliict. Lipsise, 1817, 8vo, pp. 35 — 66; C. M. Gtltat Diss, inaug. denervo 

 spnpathico. L.B. 1834, Svo, pp. 41 — 74; s.ndfiTA'N'Nivsi Das perij^herlsche Nervensijstem, 

 s- '31—143- 



