IN 1898 I directed attention to the fact that the paired elements in the front of the palate of lizards and snakes seem in all their relations to agree with the pair of bones in Ornithorhynchus, which afterwards fuse to form the dumb-bell bone, and that they cannot be homologous with the median unpaired vomer of mammals, and must have another name, and I proposed to call them prevomers. While the embryological evidence seems conclusive, the palontological testimony has not hitherto been so satisfactory as one could desire. Cynodont reptiles appear to have a single median vomer, very like that of the mammal, and one specimen of Gomphognathus shows what appear to be a pair of elements in front. Dicynodon appears to have also a single median vomer, and no paired elements. The Therocephalians, on the other hand, I have a pair of large anterior elements, and apparently no median element. With the palaeontological evidence in this condition, it is not surprising that the theory, though fully accepted by a few, and hesitatingly by others, has failed so far to be generally adopted.