The chief contributions to a knowledge of the Anomodont skull have been made by Sir Richard Owen, Professor Huxley, and Professor Cope. When Sir R. Owen published his first description of several species of Dicynodon , in 1845, and regarded that genus as indicating a new order of Saurians, an elaborate comparison was made to indicate the nature of its relation to existing orders of Reptiles, with the result that the skull was interpreted as essentially formed on the Lacertilian plan, though upon that plan structures are engrafted which are otherwise characteristic of Chelonians and Crocodiles. The Lizards with which it is chiefly compared are the fossil Rhynchosaurus of the Trias, and the existing Hatteria . The chief Lacertilian characters enumerated are:—(1) the single pre-maxillary bone and the double external nasal apertures, though the pre-maxillary is single in Chelys , and both these conditions are found in many Serpents and some Amphibians, though the great development of the pre-maxillary in Dicynodonts is thought to foreshadow its condition in Birds; (2) few existing Lizards have the maxillary arch so strong or the maxillary bones so well developed; (3) the zygomatic bone is continued from the lower border of the orbit to the upper end of the tympanic pedicle; (4) the tympanic pedicle descends vertically from the junction of the zygomatic and mastoid, and is comparatively free; (5) the flat anterior part of the parietal bone is perforated by a parietal foramen, and the posterior part of the bone bifurcates; (6) the orbits are circular and midway in the length of the skull. In some respects the characters are said to show a blending of Chelonian and Lizard structures. Thus, the palate unites features of both those orders; there is a bony floor to the orbit; the ex-occipital and basi-occipital bones combine to form the tripartite occipital condyle. Among the differences of Dicynodon from Lizards which were indicated, are:—(1) the edentulous Turtle-like mandible and pre-maxillary; (2) the expanded vertical occipital plate, which is compared to that of Crocodiles;(3) the brain-case is only two-thirds the breadth of the inter-orbital space, and in its small size suggests the lowest Amphibians; while (4) the two tusk-like teeth are only paralleled among Mammals. One of the distinctive Dicynodont characteristics is the junction of the par-occipital and sphenoid with the tympanic, near to the broad slightly convex condyle.