The Latero-Sensory Canals and Eelated Bones in Fishes. 459 



Cole and Johnstone's descriptions, is in accord with the supposition 

 that it is that bone. It is attached, at its dorsal end, to a slightly 

 raised ridge on the rounded lateral surface of the right frontal bone, 

 and a primarj" tube leaves the canal either between these two bones, 

 or enclosed in the dorsal portion of the postfrontal. The former ar- 

 rangement apparentlj^ pertains on the left side of the fish, and the 

 latter on the right side; and it will be shown, below, that the tube 

 here concerned is quite undoubtedly one half of the double primary 

 tube formed where the main infraorbital canal anastomoses with the 

 terminal tube of the supraorbital canal. 



Having traversed the postfrontal and entered the frontal bone, 

 the main infraorbital canal turns sharply backward and traverses the 

 posterior third, approximately, of the frontal. It then immediately 

 enters the squamosal (pterotic) and traverses that bone and then the 

 lateral extrascapular and suprascapular bones. As it passes from the 

 frontal into the squamosal it does not come into any direct relations 

 with the sphenotic (postorbital ossification), that bone being entirely 

 cut off from the dorsal surface of the skull by overlying portions of 

 the frontal and squamosal. This in itself shows that, in Pleuronectes, 

 the enclosing of the canal in the sphenotic (postorbital ossification) 

 must be secondary. 



Between the frontal and squamosal a primary tube is given off 

 by the main infraorbital canal, and this tube frequently undergoes 

 complete dichotomization, two independent tubes then arising from the 

 canal, one between the frontal and the squamosal (pterotic) and the 

 other in the frontal slightly anterior to its hind end. This arrange- 

 ment was found on the right side in two of the specimens examined, 

 and on the left side in a third; and the two tubes were, in two of 

 the three instances, quite widely separated from each other. No sense 

 organ was, in any instance, found in the canal between the two tubes, 

 which proves conclusively that they are simply parts of a single 

 primary tube that has undergone complete dichotomization. Near the 



I hind end of the squamosal the canal anastomoses with the dorsal 

 end of the preopercular canal, the resulting double tube arising from 

 the preopercular canal near its dorsal end. As the canal traverses 



