XIV SENSE-ORGANS 385 
subdivision of the primary pores into groups of surface-pores, 
complete the evolution of the system in its more advanced 
condition. Typically, the lateral line system consists of certain 
canals or grooves, usually but not invariably continuous, and 
defined by their innervation, (4). a /ateral canal extending along 
the side of the body and the hinder part of the head, and having 
its sensory organs suppled by the great lateralis nerve (Fig. 
220); (.) a supra-orbital canal passing forwards over the eye 
and innervated by the superficial ophthalmic branch of the 
facial nerve ; (iil.) an infra-orbital canal supplied by the buccalis 
P- $. 
mnpennn-ta 
Fic. 219.—Vertical longitudinal section through the lateral canal of Amia calva.  L.n, 
Lateralis nerve with its branches, 7, 2, to the sensory organs, s.0, 5.0; p, p, p, external 
pores ; s.c, sensory canal ; s, s, scales of the lateral line. (From Wiedersheim, after 
Allis.) 
and otic branches of the same nerve; and (iv.) a hyo-mandibular 
or operculo-mandibular canal, situated on the outer side of the 
hyoid region, and thence prolonged downward and forward in 
relation with the lower jaw, and innervated by the external 
mandibular branches of the facial nerve. The hyo -mandi- 
bular canal is sometimes distinct from the other canals, as in 
Elasmobranchs and some Teleosts (Fig. 220); and in certain 
North American Siluroids the same may be said of the supra- 
orbital. But, as a rule, the infra-orbital is continuous behind 
both with the. lateral and the supra-orbital canals, while the 
hyo-mandibular canal joins the infra-orbital, or, exceptionally, 
VOL. VII 2 C 
