The Latei'o-Sensory Canals and Related Boues in Fishes. 431 



having to that aperture the relations of the anterior end of the sub- 

 orbital portion of the main infraorbital canal of Lepidosteus, and 

 not that of the anterior end of the same canal in Amia. The canal 

 continues onward ventral to the eye, and at a certain distance behind 

 the eye turns sharply upward and so continues until it passes the 

 level of the dorsal edge of the eye. In this part of its course it 

 traverses, in succession, two bones that are suborbital, and four that 

 are postorbital in position. The anterior suborbital bone lodges three 

 sense organs of the line, and must contain the homologue of the 

 lachrymal and perhaps also that of part of the antorbital bone of 

 Amia. The second bone contains two organs, and is a suborbital 

 bone. The next bone covers the outer surface of the ventral part 

 of the cheek and lodges no sense organ, the canal simply traversing 

 its antero- dorsal corner. The next two bones lodge each a single 

 sense organ and are the regular postorbital bones of the fish. They 

 are firmly bound to each other and to the next anterior bones, but 

 loosely bound to the next dorsal bone. This latter bone lodges two 

 sense organs. It is firmly bound to the lateral edge of the skull, but 

 it overlaps externallj^ the dorsal one of the two postorbital bones, 

 and is loosely and moveably bound to it. It belongs more to the 

 dorsal than to the lateral sui'face of the skull, and it certainly is, or 

 at least contains, the homologue of the postfrontal bone of Amia. It 

 can be called the postfrontal. Immediately behind it, in line with it, 

 and apparently a posterior continuation of it, there is a smaller der- 

 mal bone which has, to the bones of the dorsal surface of the skull 

 and to those of the cheek, exactl}^ the same relations. The two 

 bones together recall somewhat the series of spiracular ossicles of 

 Polypterus. 



In the postfrontal bone the main infraorbital canal turns mesially 

 and upward, and leaving the bone traverses in succession the squamosal, 

 extrascapular, suprascapular and supraclavicular. The squamosal 

 lodges two sense organs, the extrascapular one, and the supraclavi- 

 cular one. No organ could be found in the suprascapular, but the 

 canal traversed the bone, and the two primary tubes, one at either 

 end of the enclosed section of canal, would indicate that the bone 



