THE OSTEOLOGY OF THE DIADECTIDAE 139 



The vomer. — This is a single bone of considerable vertical extent 

 which is attached anteriorly to the inner side of the premaxillaries, 

 and posteriorly either ended freely or was touched by the anterior 

 median portion of the pterygoids which met, or nearly met, in the 

 middle line. Its lower surface is marked by a double ridge of sparsely 

 set, small, conical teeth. It is impossible to trace the attachment 

 of the upper edge of the vomer. Anterior to the parietal foramen 

 there are, in the two skulls, the remnants of a descending median 

 plate, but in neither can this be traced into contact with the vomer. 

 It seems probable either that the vomer was attached to this plate 

 by a bony connection which has been destroyed, or that there was a 

 cartilaginous attachment between them. There is no trace of any 

 prevomers. It is possible that in this weak palate we have the con- 

 dition premised by those (Bland-Sutton, 1884; Broom, 1902) who 

 have contended that the true vomer is the parasphenoid developed 

 into secondary importance to supply a weakened palate. 



The premaxillaries. — It is impossible in the specimens to make 

 out the limits of these bones. Cope describes them as having short 

 and strong spines, which ascend in the median line as far as the pos- 

 terior edge of the external nares. In none is the number of teeth 

 certain, but it does not exceed four or five. They are chisel-shaped 

 incisors, evidently adapted to the cutting of pretty solid food. 



The maxillaries. — The vertical portion of the maxillaries is very 

 thin, but the alveolar surface is disproportionately widened to accom- 

 modate the alveoli for the great teeth. This alveolar edge, while 

 quite wide, is not of great vertical thickness, and stands out abruptly 

 from the side wall of the skull (formed by the vertical portion of the 

 maxillary), as a sort of shelf upon the upper surface of which termi- 

 nates the anterior end of the pterygoids and the transverse, as 

 described above. There are eleven teeth in the portion which I 

 take to be the maxillary. The posterior one is very small and peg- 

 like, but the next to the last is nearly, if not quite, the largest of the 

 series. The surfaces of the teeth are worn on the inner edge only, 

 as described by Cope. 



The palate in general. — It will be seen from the above that the 

 palate is very aberrant and in no wise resembles the palate of the 

 Cotylosauria. The bones are so closely united that it is difficult 



