The Lateral Sensory System in the Muraenidae. 163 



posterior surface of the skull, one lying' close to the foramen magnum 

 and the other considerably lateral to it. The two nerves, having' 

 issued from their respective foramina, run backward and upward 

 along the reentrant posterior surface of the skull, at the dorsal edge 

 of which they pierce, and then pass upward along, the anterior surface 

 of the aponeurosis that arises from the hind edge of the skull and 

 separates the adductor muscle from the trunk muscles. The two nerves 

 then run forward along the dorsal surface of the adductor muscle, 

 one nerve innervating the mesial half of the line of organs and the 

 other the lateral half. The nerve that innervates the latter half of 

 the line is accompanied by, or is a branch of, the nerve that inner- 

 vates the two sensory organs of the supratemporal commissure. 



On the cheek of the fish there are also two lines of the larger 

 surface organs, and one well-marked line of organs of intermediate 

 size. These latter organs form an S-shaped line near the base of the 

 gill-cover, and the nerve that innervates them could not be traced. 

 The more important one of the other two lines is noteworthy, because 

 of its relative importance and also because of its relations to the 

 underlying bones of the skull. It usually begins slightly lateral and 

 posterior to the lateral end of the middle head line of surface organs, 

 and runs directly forward about half the distance to the eye, where 

 it turns downward and backward in a curved line somewhat con- 

 centric with the hind margin of the eye. The horizontal portion of 

 this line lies practically superficial to the posterior half of the squa- 

 mosal lateral canal, the angle where the line turns downward lying 

 approximately superficial to the postorbital process of the skull. This 

 latter process, as already stated, lies about halfway between the inter- 

 orbital opening and the hind end of the skull, thus not having its ac- 

 customed relations to the eye-ball and the interorbital region. The 

 vertical portion of the line of organs, the part that is approximately 

 concentric with the orbit, thus holds a position relative to the post- 

 orbital process of the skull that the postorbital part of the main 

 infi^aorbital canal holds in the other teleostean fishes heretofore des- 

 cribed. 



The horizontal portion of the line is innervated by a nerve that 



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