Xos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 169 



found at this point in certain specimens, will be referred to in 

 describing the supraorbital canal. 



The next system on the main infraorbital line is No. 12. It is 

 represented by a single tube and pore, the tube arising from the 

 main canal as it traverses the squamosal, and running outward and 

 forward in the ridge of that bone. 



The next system, No. 13, lies near the hind end of the squa- 

 mosal, and has fused with the terminal system. No. 11, of the 

 preoperculo-mandibular canal to form a double system. It is rep- 

 resented by two tubes and pores. One of these tubes arises from 

 the main infraorbital canal at or near the point where it is joined 

 by the preopercular canal. The other arises from that part of the 

 latter canal that lies in the skin between the squamosal and the 

 upper end of the preoperculum. The first tube lies in the ridge of 

 the squamosal, issuing from the bone by the anterior one of three 

 openings in the thickened hind end of the ridge. By the second 

 hole in this thickened hind end of the bone the preopercular canal 

 enters the squamosal to join the main infraorbital canal. By the 

 third hole the main infraorbital canal leaves the squamosal to en- 

 ter the extrascapular. The double system", 13 infraorbital — 11 pre- 

 operculo-mandibular of Scomber, corresponds to system 17 infra- 

 orbital — 17 preoperculo-mandibular of Aiiiia. In Figs, i and 2 

 the tubes and pores are shown in somewhat different relations to 

 each other and to the main canal, the two figures representing 

 arrangements found in different specimens. 



The next system of the line. No. 14, is usually represented by 

 two tubes and pores, the tubes issuing from the main canal as it 

 traverses the lateral arm of the extrascapular. In Fig. 5 four 

 holes are shown in this arm of the bone. It is however probable 

 that they were not all traversed by sensory tubes, the bone here 

 being exceedingly delicate, and certain of the holes probably sim- 

 ply representing places where the bone has been incompletely 

 formed. 



System No. 15 is represented by a single tube and pore, the tube 

 leaving the main canal as it passes from the extrascapular to the 

 suprascapular. 



System No. 16 is found as one or two tubes and pores, the tubes 

 arising from the main canal near the middle of the body of the 

 suprascapular. 



