265 



strongly the appearance of being a primarily separate, somewhat cy- 

 lindrical, and slightly curved bone that has become fused secondarily 

 with the adjoining tooth-bearing part of the bone. Posterior to tube No. 7 

 the orbital edge of the maxillary is thickened, along its internal surface, 

 the bone posterior to this edge being thin, and its hind edge bearing 

 faint concentric scale-like markings. The hind edge of the bone ends 

 in two more or less distinctly marked processes, one at the dorsal 

 and the other at the ventral edge of the bone. The dorsal process 

 passes internal to the anterior end of the cheek-plate of the fish, the 

 ventral process passing external to that bone, the two bones being 

 thus firmly dovetailed together. These processes vary somewhat in 

 every specimen. The opening by which the infraorbital canal leaves 

 the dorsal edge of the posterior portion of the maxillary lies somewhat 

 in front of the overlapping anterior end of the cheek-plate. 



The hind end of the tooth-bearing part of the maxillary presents 

 a flat surface, directed backward, and against this surface the antero- 

 ventral edge of the lateral process of the ectopterygoid rests, the 

 outer, or lateral, end of that process resting against the mesial sur- 

 face of the maxillary in a short line extending dorso-posteriorly from 

 the hind end of its tooth-bearing ventral edge. The two bones are 

 here firmly bound together by a short but stout ligament that permits 

 of a little, but very little, movement between them. The anterior edge 

 of the ascending process of the splenial slides, when the mouth is 

 opened and shut, along the postero-inferior surface of the lateral pro- 

 cess of the ectopterygoid. 



The maxillary articulates, by an articular facet on the dorsal 

 surface of its anterior end, with the ventral edge of that narrow part 

 of the premaxillary that lies immediately posterior to its tooth-bearing 

 portion, the articulating surfaces not being lined with cartilage. Im- 

 mediately posterior to the premaxillary, the maxillary adjoins and is 

 bound to the lachrymal. The anterior portion of the dorsal edge of 

 the postorbital portion of the bone adjoins, and is bound to, the 

 posterior suborbital bone of Traquair's descriptions, posterior to 

 which the bone is first overlapped externally by the first bone of the 

 prespiracular series, and then by the anterior edge of the large cheek- 

 plate, or preoperculum, of the fish. 



The maxillary bone of Polypterus thus occupies a position that 

 corresponds, in many respects, to that that a bone would have that 

 was formed by the fusion of the maxillary bone of Amia and Teleosts 

 with certain of the suborbital and postorbital canal bones, and I be- 

 lieve it has always been considered as the homologue of some such 



