438 Edward Phelps Allis jr., 



Moxostoma aureolum. The canals in this fish (fig. 18) all lie in 

 the deeper layers of the dermis, each canal enclosed in a series of 

 small, short, tubular ossicles. One or more short tubules leave the 

 canal as it traverses each of these ossicles, and as each tubule opens 

 on the outer surface by but a single pore, a line of pores, lying- 

 close together, and very evident, marks the exact course and 

 position of each canal. Each and every ossicle doubtless lodges 

 one or more sense organs, for, on the internal surface of each of 

 the several ossicles that were examined, there were one or more 

 projecting tubules, each of which gave passage to a nerve. Each 

 of the main canals must therefore contain a relatively large number 

 of organs, this being an elasmobranchian rather than a teleostean 

 characteristic. 



The main infraorbital canal begins on the side of the snout 

 about halfway between the mouth and the nasal apertures, and from 

 there runs backward below and then upward behind the eye in the 

 usual manner. It then turns backward in a rounded angle, passes 

 close above the dorsal end of the opercular opening, turns downward 

 along the hind edge of that opening, and at about the horizontal 

 level of the anterior, suborbital part of the line turns backward as 

 the lateral line of the body. In the suborbital, and the ventral two 

 thirds of the postorbital part of its course, the tubular ossicles that 

 enclose the canal lie directly upon the external surface of, and are 

 firmly bound to, but only in places ankylosed with a series of underlying 

 membrane bones. These latter bones are thin and flat, and certainly 

 represent a separate, membranous component of the lachrymal, sub- 

 orbital and postorbital bones. Dorso-posterior to the dorsal postorbital 

 bone the canal passes onto the outer surface of the dilatator oper- 

 culi muscle, and the enclosing ossicles are here widely separated, by 

 that muscle, from the underlying bones of the skuU, Posterior to the 

 dilatator muscle the canal comes in contact with the projecting 

 posterior edge of the auto-squamosal (pterotic), and is firmly attached 

 to it by membrane. It then passes superficial to the levator operculi 

 muscle, and beyond that muscle turns downward behind the opercular 

 opening; the enclosing ossicles here lying slightly behind and concen- 



