Structure and Affinities of the Endoihiodont Reptiles. 265 



left quadrate. In the type specimen the lower jaw as well as the 

 snout is very badly crushed, and the extreme massiveness of 

 the jaws is not readily appreciated. Though the mandible differs 

 considerably from that of either Dicynodon or Oudenodon, it agrees 

 rather more with the former than with the latter. In the tusked 

 Dicynodon the front of the lower jaw is much compressed to allow 

 it to pass between the long tusks, and as is the case in the sabre- 

 toothed tigers, the anterior part of the jaw is greatly deepened. In 

 Oudenodon the front of the jaw is much broader than in Dicynodon 

 and relatively less deep, but otherwise the tw^o closely resemble 

 each other. In Endothiodon the jaw, though essentially similar 

 in structure to that of the other Anomodonts, is different in front 

 from that of either Dicynodon or Oudenodon in being much more 

 powerfully built. 



The two dentaries, which are anchylosed, make with one another 

 an angle like the letter V. There is little doubt that the jaw in 

 front has ended in a sharp upturned point which fitted into the 

 V-shaped depression in the front of' the upper jaw. The upper 

 border of each dentary behind the pointed portion has two parallel 

 ridges about 12 mm. apart, and inside of the second ridge are the 

 teeth. There is one main row of teeth which has, especially towards 

 the hinder part, an irregular second row of smaller teeth inside 

 and another imperfect row of small teeth outside. The symphysis 

 of the jaw is mainly formed by the powerful splenials, which are 

 anchylosed together, and apparently also anchylosed to the den- 

 taries. A little behind the symphysis each dentary is separated 

 from the splenial by the angular passing forward between them. 

 Immediately outside of the anterior part of the angular the dentary 

 is very much thickened, forming a very marked tuberosity. It is 

 highly probable that practically the whole of the outer surface 

 dentaries has been covered by a horny sheath. 



Though Seeley (6) in his account of the lower jaw says nothing 

 of the structure, it is possible from his figure to obtain some idea of 

 the bones forming the posterior part. In the post-dentary portion 

 he shows that there is a deep excavation on the outer side and 

 figures a suture crossing it from above downwards and backwards. 

 There is little doubt that the bone above the suture is the sur-angnlar 

 and the lower bone the angular. The depression is somewhat 

 similar to the depression in the jaw of Oudenodon trigoniceps. The 

 articular region is described by Seeley as " convex from above down- 

 wards, wider above than below, and deeper than wide ; it measures 

 7 cm. deep by 4 cm. wide as preserved, but may have been heart- 

 shaped, with a concavity indenting the superior border. Its lateral 



