NERVES OF FISHES. 303 



ganglion (Gasserianum). In the Skate (Eaia) the roots of the 

 two ganglionie portions, fig. 202, a, b, of the trigeminal, arise from 

 the restiform tract : the non-gangl ionic part, c, from the folded or 

 fimbriate part of the tract. A pin is passed between the second 

 ganglionic and the non-ganglionic portion ; the latter, c, being re- 

 flected back on the left side of the figure ; on the right side the 

 non-ganglionic branches, e, f, are left, accompanying the corre- 

 sponding branches of the ganglionic portion, a, e, f The acoustic 

 nerve, 7, comes off as a branch of the second ganglionic part of 

 the trigeminal. 



In Osseous Fishes the hindmost branch of the fifth nerve divides, 

 one part descending to the ' opercular ' nerve, fig. 203, t, the other 

 ascending to the ' lateral ' nerve, ib. m ; but both receiving an acces- 

 sion from other sources to form those nerves respectively. A branch 

 of the vagus, fig. 202, t, ascends forward to join the fifth in 

 forming the dorsal division of the ' nervus lateralis,' ib. m, which 

 escapes by a foramen in the parietal bone ; the rest of the fifth 

 emerges from the skull by a hole (Carp), or a notch (Cod), of the 

 alisphenoid. The lateral nerve in the Cod is formed chiefly by 

 the fifth, fig. 196, 5, and receives only a slender filament of the 

 vagus. In the Carp the vagus chiefly forms the lateral nerve. 

 In the Cod, fig. 205, the lateral nerve first sends off a branch, ib. l, 

 which runs along the sides of the interneural spines, receiving 

 branches from all the spinal nerves ; it then curves down along 

 the scapular arch, gives branches to the pectoral, ib. P, and ven- 

 tral, ib. v, fins, supplies the great lateral muscular masses, ib. 2, 

 and the mucous canal, ib. 3, and sends a nerve, ib. 4, to the inter- 

 haemal spines, which communicates with filaments from the corre- 

 sponding spinal nerves : both interneural and interhremal branches 

 terminate in the plexus supplying the caudal fin : thus all the 

 locomotive members are associated in action by means of the 

 nervi laterales. The mandibular division of the fifth (ramus man- 

 dibularis, seu maxillaris inferior} consists chiefly of motory filaments 

 which supply the muscles of the hyoid and mandibular arches, 

 and the ' ramus opercularis seu facialis. ,' fig. 202, t, to those of the 

 gill-cover ; the sensory filaments go to the teguments of the sides 

 of the head, ib. r, and under jaw, enter the dental canal, supply 

 the teeth, and, in the Cod, the symphysial tentacle. 1 The maxil- 

 lary division (r. maxillaris) bifurcates behind the orbit, one branch 

 passes outward to supply the suborbital mucous canals and integu- 

 ments on the sides of the head ; the other, after sending a branch 

 obliquely outward, curves forward along the floor of the orbit, 



1 CCXXVI. p. 45, fig. 2. 



