The Latero-Sensory Canals and Eelated Bones in Fishes. 437 



enclosed in a small bone that morphologically formed part of the 

 frontal, but was not completely fused with the remainder of that bone. 

 The outlines of the mesial extrascapular ossicle, although that 

 ossicle was inseparably fused with the adjoining or perhaps underlying 

 parietal, were easily traceable. 



Cyprinidae. 



Carassius auratus. Fig. 17 shows the course of the canals in 

 this fish, and also their relations to the cranial bones. 



The dorsal one of the chain of infraorbital bones is evidently the 

 dermal postfrontal of the fish, and it here has a postfiontal rather 

 than a postorbital position. 



The supratemporal canal leaves the main infraorbital canal as 

 that canal traverses a small triangular extrascapular, and, running 

 mesially, traverses the hind border of a parieto-extrascapular to unite, 

 in the mid-dorsal line, with its fellow of the opposite side of the head. 



The supraorbital canal anastomoses, by what is probably its pen- 

 ultimate primary tube, with the main infraorbital at the bend where 

 the latter canal passes from the postfrontal bone into the squamosal. 

 The terminal pore of the canal lies at or near the suture between 

 the frontal and the parieto-extrascapular, the canal not entering the 

 latter bone at all. 



The preopercular canal, as it passes from the dorsal end of the 

 preoperculum to join and anastomose with the main infraorbital in the 

 squamosal, traverses the dorso- anterior comer of the operculum. But 

 this section of the canal is certainly secondarily and not primarily 

 enclosed in the operculum, for no slightest indication of a sense organ 

 could here be found. 



Sagemehl says [65, p. 507j, as has already been stated, that, in 

 the Cyprinidae, as in the Characinidae, the main canal is widely 

 interrupted (breit unterbrochen) between the hind corner of the frontal 

 and the front corner of the squamosal, by the "post frontale", which 

 latter bone pushes in between the other two bones. This is certainly 

 not true of Carassius any more than of the three species of Chara- 

 cinidae examined, and it will be shown to be not true of Moxostoma also. 



