432 Edward Plielps Allìs jr., 



lodged an organ. Elsewhere a primary tube left the canal regularly 

 between each two adjoining organs. 



As the canal traverses thß squamosal, Mr. Nomura found that it 

 anastomosed with the hind end of the supraorbital canal, the anasto- 

 mosis taking place between the two squamosal organs, and the resul- 

 ting double system being represented by two surface pores. Sage- 

 mehl [64] does not give this anastomosis in any of the species he 

 particularly describes, the hind end of the supraorbital canal, as shown 

 by him, approaching but not anastomosing with the hind end of the 

 main infraorbital; and the same arrangement seemed to be presented 

 also in a prepared skull of Macrodon that I examined most cursorily 

 while at Sth. Kensington. It may therefore be that there is not uni- 

 formity in the arrangement here. The double pore found by Mr. Nomura 

 where the two canals anastomose, lies somewhat anterior to the line 

 produced of the preopercular canal, but it is at a corresponding pore, 

 in Hydrocyon and Alestes, that the latter canal anastomoses with 

 the main infraorbital. The anastomosis of these two canals is 

 apparently prevented, in Macrodon, by the interposition of the dermal 

 bone that lies immediately posterior to the postfrontal. In Polypterus 

 the posterior spiracular and the post-spiracular ossicles hold a similar 

 position and similar relations to the two canals, and it is an evident 

 supposition that the series of spiracular bones of this fish plus the 

 dermal component of its so-called postfrontal are the homologues of 

 the postfrontal and next posterior bone of Macrodon. That squamosal 

 organ of Macrodon that lies anterior to the point of anastomosis of 

 the supra- and infraorbital canals is innervated by the ramus oticus; 

 the one that lies posterior to it, by an anterior branch of the supra- 

 temporal branch of the nervus lineae lateralis. 



The supraorbital canal begins at a single pore that lies almost 

 directly anterior to the anterior nasal aperture. From there the canal 

 enters at once the nasal and traverses that bone, and then the 

 anterior two-thirds of the frontal, in a nearly straight line. The 

 canal then takes a short sharp turn laterally, then turns backward 

 again, traverses the i-emaining part of the frontal, enters the parietal, 

 at its anterior edge, and curving laterally leaves the parietal at its 



