220 



OSTEICHTHYES 



on to the head. By a subdivision and branching of the pore canal 

 a number, of small pores may replace the original primary pore. 



We have already seen (p. 125) that the canals of the lateral- 

 line system follow a fairly uniform course on the head in the 

 various groups of fish. The Elasmobranchii and Osteichthyes agree 

 well in this respect (Allis [9, 19], Garman [148], Clapp [78], Herrick 

 [210], Collinge [85-89], etc.). Now the connection established 

 with the cranial bones is as follows (Figs. 196, 500, A). The trunk 

 lateral line passes by means of the post-temporal on to the supra- 

 temporal or the pterotic (squamosal) ; from this point a transverse 



lac 



FIG. 193. 



Leuciscus ccphalus, L. A, longitudinal section through the skin, scales, and muscles. 15, 

 surface view of body-wall ; the skin has been removed on the left, and the myotomes exposed 

 below on the right, c.t, connective tissue ; op, epidermis ; l.sc, lateral-line scale : w, myotome ; 

 o, opening of lateral-line canal ; ae, scale in connective-tissue pocket ; .</,, skin. 



branch is often sent off towards the middle line running as a rule in 

 the supratemporal bones it may be called the supratemporal or 

 occipital branch. The organs in this region of the canal are supplied 

 by the supratemporal twig of the vagus. The main line then con- 

 tinues horizontally through the pterotic, forming a short temporal 

 canal supplied by the otic branch of the glossopharyngeal (this 

 short region does not always occur). The canal is prolonged 

 forward to behind the orbit postorbital line through the pterotic 

 and post-frontal. It is supplied by the otic branch of the facialis. 

 Next it passes below the orbit and forwards to the nostrils ; the 

 ramus buccalis facialis supplies this infraorbital canal, which passes 

 through the post-, infra-, and preorbital ('lachrymal') bones. 

 Starting from the junction between the postorbital and infra- 



