Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 269 



to the anterior edge of the preoperculum, or immediately in front 

 of that edge, and while in that position gives off two or three 

 branches, one of which is the ramus mandibularis internus. The 

 larger of the other two branches, in the one specimen in which 

 it was traced, ran downward and forward along the external sur- 

 face of the quadrate and disappeared in the dermal tissues near 

 the articular end of that bone. The other branch ran downward 

 and inward internal to the preoperculum. That part of the truncus 

 that remains after giving off these branches is the ramus man- 

 dibularis externus, but it seems not to be composed entirely of 

 lateral sense organ fibers, as it apparently was in Auiia. 



The Ramus Mandibularis Externus {mef), having reached 

 the inner surface of the palato-quadrate, runs downward and for- 

 ward internal to the anterior edge of the preoperculum, or in- 

 ternal to the adjoining hind edges of the quadrate and symplectic, 

 and here gives oft^ either two or three branches, this varying in 

 different dissections that were made. Two of these branches, 

 where there are three, or both of them where there are but two 

 enter the preoperculum and supply organs 9 to 6 of the pre- 

 operculo-mandibular lateral canal. The third branch, noticed 

 in two or three specimens but only traced in one, arose between the 

 two sense organ branches, ran downward and backward along the 

 inner surface of the preoperculum, and then onto the lateral 

 surface of the interoperculum, between that bone and the pre- 

 operculum. There it separated into two parts, one of which ran 

 forward and the other backward along the lateral surface of the 

 interoperculum, between that bone and the preoperculum. This 

 branch corresponds, approximately, in its origin from the main 

 nerve, to the branch sent in Amia to the vertical cheek line and 

 mandibular line of pit organs. No indication whatever of sur- 

 face sense organs could however be found in this part of the head 

 of Scomber. 



After giving 'off these two or three branches the mandibularis 

 externus continues downward and forward along the inner sur- 

 face of the quadrate and symplectic, crosses the lower end of the 

 quadrate, internal to its articular head, and reaches the mesial sur- 

 face of the articular. In this part of its course it passes between 

 the preopercular and quadrate heads of the tendon that arises 



