NERVOUS SYSTEM OF FISHES. 199 



roots of the spinal nerves in Osseous Fislies, is tliat given by ]Mi'. 



Swan from the Cod. * Tlie dorsal root sends a filament (yfig. 56. a) 



upwards, which joins a ventral filament {h) from the preceding nerve, 



-^ and forms the ' ramus dorsalis ' (rf) : the dorsal root 



sends two filaments (c) downwards, which unite to- 



^r^ I gether, and with a ventral filament (e) of the same 



^^m ' ^ nerve to form the ' ramus ventralis ' iv). The fila- 



-^ ment of the ventral root sent to the ramus dorsalis 



// of the succeeding nerve perforates the lower division 



/ , /-^ of the dorsal root of its own nerve. Thus each spinal 



nerve forms a dorsal and a ventral branch ; the 



laraus dorsalis includes a sensory filament of its own 



^ s^ <^ nerve, and a motory filament of the antecedent nerve : 



\^ \ {" the ramus ventralis is formed by a motory and a 



sensory filament of its own nerve ; both rami ' ven- 



connections ot spinal tralcs ' and ' dorsalcs ' are associated together, and 



and lateritl nerves, ° ' 



Cod. (Mr. Swan.) y^\\\\ the Vagal and trigeminal nerves through the 

 medium of the great ' nervus lateralis.' 



The roots of the nerves distributed to the free, exploratory, 

 pectoral rays of the Gurnards, rise from special ganglionic swellings 

 of the cervical portion of the dorsal myelonal columns. 



Sympathetic. — In the Myxinoid Fishes this nerve, or system of nerves, 

 is represented by the intestinal branch continued from the confluence 

 of the two nervi vagi. The best illustrations of the sympathetic in ordi- 

 nary Osseous and Plagiostomous Fishes are those given by Mr. Swan, 

 from the Codf and the Skate. | Each trunk of the nerve extends 

 in Osseous Fishes, from the side of the basis cranii (not entering the 

 cranial cavity) to the tail, accompanying the aorta along the hasmal 

 canal. Its fii-st or anterior communication is with a branch of the 

 fifth, and a filament is sent forward to the ciliary ganglion ; and, in 

 the Carp a filament joins the abducent nerve, to which Cuvier 

 thought he had also traced a filament of the sympathetic in the Cod : 

 the sympathetic next communicates with that anterior portion of 

 the vagus (the glosso-pharyngeal ?) which joins part of the acoustic 

 nerve, and supplies the first partition of the gills : the sympathetic 

 trunks also receive accessions from the trunks of the vagus ; and, 

 converging, intercommunicate by a cross brancli : they then send 

 nerves which join the gastric branches of tlie vagi, in order to form 

 or join a splanchnic ganglion and plexus on the mesenteric artery 

 from which plexus branches are sent to the intestines, pancreas, and 

 spleen. The sympathetic trunks are continued on each side of the 



* Liv. pi. viii. \ lb. pi. vi. \ Il>. pi. i.v. 



o 4 



