72 The Ottawa Naturalist. [October 



process. Anteriorly it overlaps the thin, lower posterior termination 

 of the dentary. Postero-internally the main portion of the bone 

 extends thinly backward, facing upward and inward beneath the 

 articular. Toward the inner border a thin flange, rising from the 

 upper surface passes forward external to the articular. The mandi- 

 bular cotylus occupies the postero-external angle of the main portion 

 of the bone. 



Articular. This element, as yet not fully known, is higher than 

 broad, thinnest below in its more posterior part, and extends forward 

 as a moderately thin bone wedged in between the surangular and the 

 outer face of the splenial. Below it is supported by the surangular. 

 Supero-externally it supplies a surface as its contribution to the 

 mandibular cotylus. The bone is preserved, in part, both in the type 

 skull, and in the disarticulated skull, Cat. No. 2289. 



Dentary. Is large, with three-eighths of its length in front 

 edentulous, deeply excavated posteriorly by the mandibular fossa, and 

 with the dental magazine occupying nearly one-half the length of the 

 bone. The coronoid process is robust and placed far back. The 

 dentary attains its greatest breadth across this process. For the full 

 length of the magazine it is deep and moderately thick. The edentulous 

 part is comparatively thin with a gradually lessening depth forward, is 

 longitudinally concave internally, and curves abruptly inward in 

 front, with a lowering of the superior border, to -meet the opposite 

 dentary in a ligamentous connection behind the predentary. The 

 mandibular fossa excavates the coronoid process behind, and in- 

 ternally is continuous with the Meckelian groove which lessens in 

 depth in its forward course near the lower border of the bone, and 

 disappears in advance of a point in line with the front end of the 

 magazine. Behind the magazine the dentary ends in a laterally com- 

 pressed, pointed process, internal to the mandibular fossa. This pro- 

 cess is covered on its inner face, and embraced above, by the anterior 

 end of the splenial. Posteriorly, beneath the Meckelian groove, is a 

 narrow surface marking the internal application of the angular as far 

 forward as a point nearly beneath the midlength of the magazine. 

 Posteriorly below the dentary is transversely broad, thin and obtusely 

 pointed at its termination, underlapping the surangular so that the 

 floor of the mandibular fossa is continuous with the upper front sur- 

 face of the surangular. The narrow symphysial surface is deeply 

 grooved from front to back. The dental foramina, corresponding in 

 number to the vertical series of teeth, are conspicuous internally below 

 the magazine. At the anterior end externally is a rather large foramen 

 behind which are six or seven smaller ones at irregular intervals back 

 to the front of the magazine. Still farther back are a few other 

 foramina in the outer face of the bone. 



