Reptilian Lower Jaws, 579 



opposite side in a relatively large symphysis. Its position in 

 the figure Biay be slightly misplaced, being that which it now 

 occupies in the somewhat disturbed jaw. The posterior 

 narrow part of the bone is separated by a wide ciack, and 

 may conceivably be a somewhat misplaced part of the pre- 

 articular. 



The coronoid is a very thin bone whose shape is shown in 

 the drawing l}'ing on tlie inner aide of the dontary in the 

 position shown. 



The surangular is a very thin sheet of bone whose outer 

 surface is almost entirely overlapped by the angular. Poste- 

 riorly it thickens and is united with the articular by a visible 

 suture, its hinder edge overhanging the outer part of the 

 articular facette. 



The angular is a large thin bone overlapping the surangular 

 and itself overlapped in front by thedentary. It is strength- 

 ened by a narroAv rib which crosses its outer surface diagonally, 

 and its low^er border has a deep notch which is overhung by 

 a reflected lamina exactly as in Dicynodon. 



The articular is a small bone, triangular in shape when 

 viewed from above, whose outer face is covered by the sur- 

 angiilar. The base of the triangle is formed by the articular 

 facette, which is directed backwards and very slightly 

 upwards. The inner and lower faces of the bone are covered 

 anteriorly by the prearticular. The lower side of the bone 

 bears a very small and reduced postarticular process. 



The prearticular is a long bone, flat anteriorly, but bearing 

 a prominent ridge behind where it covers the articular, from 

 •which it is very obviously distinct in the specimen. 



Cynodontia. 



The lower jaw of Cynognathus has been described by 

 Seeley, whose description is, as usual, quite accurate, although 

 hard to follow in the absence of intelligible figures. Most of 

 his determinations of individual bones, although offered with 

 great reserve, are also accurate. Broom has also described 

 the type, but his reading of its structure is not quite correct. 



The following account is founded on the perfectly preserved 

 and prepared lower jaw of the type specimen of Cynognathus 

 crateroiwtus, but I have compared it with all the other known 

 specimens of higher Cynodonts. 



The dentary is a very large bone fused with its neighbour 

 at the powerful symphysis, produced backward into an enor- 

 mous coronoid process and overlapping all the other bones of 

 the jaw. 



