222 



BONY FISHES 



vii. 19- 



Fig. 138. Diagram of ventral view of the 

 sympathetic system of the front part of the 

 body of Uranoscopus, showing the fibres 

 in the sympathetic and oculomotor that are 

 responsible for the light reflex. 

 (From Young.) 



cil.brev. cil.long., short and long ciliary nerves; 

 cil.gn., ciliary ganglion; dors.r. dorsal root; dil. 

 dilatator muscle; hypo, hypoglossal; n.splanch. 

 splanchnic nerve; opt. optic nerve; p. pupil; 

 pal. VII, palatine branch of facial ; prof, profun- 

 dus; r.b. short root of ciliary ganglion; r.comm. 

 ramus communicans; r.l. long root of ciliary 

 ganglion; sph. sphincter muscle; ventr.r. ven- 

 tral root; 1II-X, cranial nerves with their 

 sympathetic ganglia (V.symp. &c.); VII hyo. 

 hyomandibular branch of facial; r— 4 sp.symp. 

 spinal sympathetic ganglia. 



19. Touch 



Touch is, of course, well 

 developed in fishes, and in many 

 species there are special sensory 

 filaments, which presumably serve 

 this sense. They are usually de- 

 veloped around the mouth, as in 

 the catfish; in other fishes they 

 are modifications of the fins, for 

 instance, the pectoral fins of 

 gurnards, which also contain 

 chemoreceptors. 



20. Autonomic nervous system 



The autonomic nervous system 

 of bony fishes is organized on a 

 plan rather different from that 

 both of elasmobranchs and of 

 land animals. There is a chain of 

 sympathetic ganglia, extending 

 from the level of the trigeminal 

 nerve backwards, a ganglion 

 being found in connexion with 

 each of the cranial dorsal roots 

 (Figs. 138 and 139). These gan- 

 glia do not receive pre-ganglionic 

 fibres from the segments in which 

 they lie, but by fibres that run out 

 in the ventral roots of the trunk 

 region and thence forwards in the 

 sympathetic chain. This emer- 

 gence of the pre-ganglionic fibres 

 for the head in the trunk region 

 recalls the arrangement in land 

 animals. 



Each trunk sympathetic gan- 

 glion, besides receiving a white 

 ramus communicans of pre-gan- 

 glionic fibres from its spinal nerve, 

 also sends a grey ramus back to 



