Prof. Owen on the genus Dicynodon. 69 



is one inch and one-third ; at the fore-part of the symphysis it seems to have in- 

 creased to the depth of two inches, hut the apex is broken away. The lower border 

 of the jaw is shghtly concave : the angular process appears to have been continued 

 but a very little way beyond the articular cavity, which is excavated on the pos- 

 terior surface, sloping from the coronoid eminence backwards to the angle. That 

 eminence, which is developed from the coronoid or complementary piece (26 a), is 

 low and long, and rises behind the middle of the ramus. A strong ridge projects 

 from the outside of the jaw, extending along the middle third of the ramus, equi- 

 distant from the alveolar and the lower borders of the jaw (PL IV. figs. 3 & 6, 24). 

 Anterior to the coronoid the upper border of the jaw rises with a gentle concave 

 curve as it advances forward to meet and join the opposite border at the upper 

 extremity of the strong and vertically extended symphysis : the fore-part of the 

 symphysis is convex from side to side, three-fourths of an inch broad, and slopes 

 from below upwards and forwards with a gentle convex curvature, without any 

 trace of median suture. It is divided by a slight ridge on each side, externally, 

 from the concavities receiving the tusks when the mouth is closed. 



On the right side of the lower jaw, attached to the cranium,^ the posterior pointed 

 extremity of the fractured remains of the angular piece (PI. III. fig. 1, 26), may be 

 clearly traced, terminating about half an inch in advance of the glenoid articulation : 

 this is supported by the articular piece (25), which forms exclusively the small 

 angular process behind and below the joint for the attachment of the digastric 

 muscle. The outer wall of the left ramus is broken away so as to expose the outer 

 surface of the anterior part of the articular piece, which extends forwards upon the 

 inner side of the ramus in a pointed form nearly half-way towards the symphysis, 

 where it joins the opercular or splenial piece, 25 a. 



The sur-angular extends from the articulation forwards, beneath the large com- 

 plementary or coronoid piece, terminating gradually in a point between that and 

 the dentary. It is cut across near this extremity at 25 in fig. 6. PI. IV. ; and the 

 trihedral form of its thicker posterior part is shown at 25 in fig. 5, 



The coronoid or complementary piece, 26 a, is a large bone, forming the upper 

 border of the middle two-thirds of the ramus. It commences by a point posteriorly, 

 which rests upon both articular and sur-angular pieces ; gradually enlarges, chiefly in 

 the vertical direction, as it extends forwards ; is grooved upon its upper thin border, 

 and more widely and deeply excavated below, where it receives the tapering anterior 

 extremity of the sur-angular : both grooves are shown in the section PI. IV. fig. 6, 

 through near the middle of the ramus at 26 a : the slender posterior end of the 

 coronoid piece is cut through at 26 a in fig. 5. The angular piece, which forms no 

 part of the angle of the jaw in Dicynodon any more than it does in modern Lizards, 

 extends from beneath the articulation along the lower border of the jaw, increasing 



VOL. VII. SECOND SERIES. L 



