The Lateral Sensory System in the Muraenidae. 157 



operculum the canal is enclosed in a long tube of the fibrous and 

 fibro-cartilaginous tissue characteristic of the fish, and at its dorsal 

 end it joins the infraorbital, supratemporal, and lateral line canals in 

 the manner alreadj^ described in describing those several canals. 



In the preopercular canal there are four sense organs, Nos. 8 

 to 11 of the line, three of them lodged in the preoperculum and 

 one in the long tubular structure that lies dorsal to that bone. Be- 

 tween each two of these four organs there is a large pouch, direc- 

 ted backward and downward, these pouches representing primary tubes 

 9, 10, and 11 of the line. Tubes 9 and 10 open on the outer surface 

 by a single pore, while tube 11 is blind. Considerably dorsal to these 

 three pouches, in the angle between the canal and the canal of the 

 lateral line, there is another blind pouch, directed backward and 

 downward and representing the compound tube formed at the point 

 where the preopercular canal joins the infraorbital, supratemporal, and 

 lateral line canals. 



Supratemporal cross-commissure, and lateral canal of the body. 



The supratemporal cross-commissure extends across the dorsal 

 surface of the fish, practically immediately dorsal to the hind end of 

 the skull. It extends from the anterior end of the lateral canal of 

 one side to the corresponding end of the canal of the other side, and 

 lies in a groove that separates the muscles of the head from those 

 of the trunk. It contains four sense organs, two on each side, the 

 organs lying in cylindrical tubes that are partly of bone and partly 

 of fibro-cartilage, and that lie in the outer edge of the tough aponeu- 

 rosis that rises from the hind edge of the skull and separates the 

 muscles of the head from those of the trunk. Between the two tubes 

 on each side, there arises from the dorsal surface of the commissure 

 a primary pouch which extends forward a short distance in front of 

 the commissure and backward a considerable distance behind it. This 

 pouch is usually blind, but a pore sometimes opens from its hind end 

 on to the outer surface of the body. In the mid-dorsal line of the 

 I body another but smaller pouch arises from the dorsal surface of the 

 commissure and extends both forward and backward of it, the forward 



