THE CRANIAL NEKVES AND LATERAL SENSE ORGANS OF FISHES. 



121 



(3) A hyomandibular or operculo-mandibular canal. Developed in connection witJi 

 the lower jaw, and may be represented by one or more canals. Innervated by the external 

 mandibular lateral line nerve. Ventrally may anastomose with its fellow or fellows of 

 the opposite side, but usually ends blindly ; dorsally usually anastomoses with the infra- 

 orbital canal, may in some cases do so with the lateral canal, may anastomose with botli 

 these canals, or may remain independent of any. 



Figure of Gadus virens. half natural size, showing the sensory canals and their innervation — the latter imlicatefl by 

 the different kinds of shading. D.F. anterior extremity of dorsal fin; Z,'. supra-temporal portion of lateralis 

 canal ; L\ lateral portion of lateralis canal ; iV\ anterior and posterior narial openings ; 0. opercular fold ; 

 PcT.F. pectoral fin; Plv.F. pelvic fin; P.O. pit orgms (innervated by the lateral line nerves) ; S.O.C. supra- 

 orbital commissure. 



(1) Supra-orbital canal, S.O. Innervated by superficial ophthalmic lateral line nerve — eroBS-hatched. 



(2) Infra-orbital canal, F.O. Innervated by buccal + otic lateral line nerves — dotted. 



(S) Hyomandibular or Operculo-mandibular canal, H. Innervated by external mandibular lateral line 



nerve — longitudinal shading. 

 (4) Lateralis canal, D and L'^. Innervated by lateralis lateral line nerve — oblique shading. 



(4) A lateral canal situated at the side of the body. Innervated by the lateralis 

 lateral line nerve. Anteriorly anastomoses usually with the infra-orbital canal only, 

 but may also do so with the supra-orbital canal ; posteriorly ends blindly at the tail. 

 The canal known as the supra-temporal or occipital commissure ( = Commissural canal of 

 Ewart) has somewhat variable relations, and is perhaps not homologous in all fishes. 



