[ ^15 J 
VI. Researches on the Structure, Organization, and Classijication of the Fossil 
Jie^ytilia. — 
VI. On the Anomodont Regotilia and their Allies. 
By H. G. Seeley, F.R.S., Professor of Geography in King's College, London. 
Eeceived June 20,—Read June 21, 1888. 
[Plates 9-25.] 
The Structure of the Skull in Jinoraodontia. 
The chief contributions to a knowledge of the Anomodont skull have been made by 
Sir Richard Owen, Professor Huxley, and Professor Cope. When Sir Pt. Owen 
published his first description of several species of Dicynodon,\x\ 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 jilan, 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 :—(l) the single pre-maxillary bone and the double external 
nasal apertures, though the pre-maxillary is single in Chelys, and both these con¬ 
ditions are found in many Serpents and some Amphibians, though the great develop¬ 
ment of the pre-maxillary in Dieynodonts is thought to foreshadow its condition in 
Birds ; (2) few existing Lizards have the maxillary arch so strong or tire 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 compara¬ 
tively free; (5) the flat anterior part of the parietal bone is perforated by a parietal 
foramen, and the posterior part of fhe 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 Dicynod.on from Lizards which were indicated, are;—(l) the 
* ‘ Geol. Soc. Trans.,’ vol. 7. 
2.12.89 
