22 



NERVE COMPONENTS 



to the development of the 'end-organs' they supply. Some 

 systems may increase in importance ; others may dwindle or dis- 

 appear altogether. Thus, the splanchnic components, so small in 

 the spinal nerves, are much developed in the head-region ; the 

 acustico-lateral system, so extensive in the fish, survives only in the 

 ear of the land vertebrate. 



We may now briefly analyse the nerves of a fish into their chief 

 components (Fig. 12). A typical spinal nerve is formed by the 

 junction of a dorsal ganglionated root, containing a large general 



bll 



MX. 



FIG. 12. 



Diagram of the nerve-coniiwnents in the head -region of a fish (chiefly after the figures of 

 Ilerrick). ., rainns lateralis accessorius (r. rerurrens f:u:ialis, r, ace. vagi); cb, abducens 

 (0); an, anastomosis between facial and glossopharyngeal ; au, auditorius (8); lit, r. buccalis 

 (7);/o, v. ophthalmicns superflcialis (7); g, branchial slit; gl, glossopharyngeus (i 1 ) ; h, r. 

 hyoinandibularis (7)'; iv, r. intestinalis (10); lv, r. lateralis (10); mrt, r. mandibularis (5); 

 mx, r. maxillaris (5) ; oc, motor ocrili (3) ; or, outline of orbit ; p, patheticus (4) ; pa, r. pala- 

 tiimg (7); pr t profundus ; jyrt, r. pretreinaticus (10); 2 )S 7'> r - pretrematlcna (7); pt, r. post- 

 trematicns (10) ; rd, r. dor.salis ; ?/, r. reourreiiR (7) ; f.g, spinal ganglion ; stv, r. supra- 

 temporalis (10); tg, r. sapratemporalis (0); to, r. optliahnicus snperficialis (5) ; v.r, ventral root 

 of spinal nerve. Between the vagus and the first spinal nerve are some spino-occipital ncfveH 

 (ventral roots). The numbers refer to tlie cranial nerves. For the explanation of the 

 components see Fig. 100, p. '_'-2'2. 



cutaneous component and a small splanchnic motor and sensory 

 component, with a ventral root of somatic motor fibres. The mixed 

 nerve branches, so that the general cutaneous and the somatic 

 motor nerve -fibres are distributed along three main trunks, the 

 ramus dorsalis, ramus medius, and ramus ventralis, to the dorsal fin 

 muscles, dorsal somatic and ventral somatic muscles respectively, 

 and to the corresponding regions of the skin. The paired fins are 

 supplied from branches of the rami ventrales. The splanchnic 

 components pass into the sympathetic system by the ventral 

 ramus communicans. 



