62 Prof. Owen on the Reptilian Fossils of South Africa. 



DiCYNODON LACERTICEPS. 



Commencing with the most perfect of the fossil skulls *" which have at present 

 been worked out of the hard matrix, the longer and narrower facial part which it 

 presented, in comparison with the others, suggested to me the term ' lacerticeps,' 

 lizard-headed, for the species to which it belonged. 



The occipital region of this skull (PI. IV. fig. 2.) is well-preserved, and is formed 

 by a moderately broad, triangular, vertical, continuous wall of bone, overhung by 

 an angular horizontal ridge, about half an inch in breadth, and shaped like the 

 penthouse of a gable-end; this ridge is formed by the supra-occipital (4), the 

 parietal (8), and the mastoid (7) bones. 



This character is peculiar, as has been already observed, to the Crocodilians 

 among existing Reptilia. The Chelonians all present a strong and long spine 

 developed backwards from immediately above the foramen magnum. The Lacertians 

 and Ophidians have two wide vacuities in the occipital region over-arched by the 

 elongated mastoids, which in Serpents are prolonged backwards. In the Batra- 

 chians the low and narrow occipital region slopes directly forwards from the great 

 foramen, and presents also another and more decisive difference in the two con- 

 dyles for the articulation of the head with the vertebral column and their lateral 

 position in respect of the occipital foramen. 



This foramen (m) in the Dicynodon lacerticeps, is vertically oval, with the large end 

 downwards : its lower fourth part is bounded by a single subhemispherical, convex, 

 articular condyle, which was partly broken away in the specimen. The upper angles 

 of the condyle are separated by a smooth depression from two small obtuse promi- 

 nences, projecting one on each side the middle of the great foramen, immediately 

 below the suture which divides the ex-occipitals (2, 2) from the supra-occipital (4). 



On the fractured surface of the occipital condyle we perceive two fine lines of 

 the matrix, commencing from near the middle of its upper border which forms the 

 lower part of the foramen, and diverging as they descend, dividing the osseous 

 substance of the prominence, like veins traversing a rock, into three equal parts. 

 These veins of matrix mark the sutures between the basi-occipital (1) and ex-occi- 

 pitals (2, 2), which three elements enter, in the same proportions, into the forma- 

 tion of the condyle as in the existing Lizards. 



In the Crocodiles the single condyle is formed almost exclusively by the basi- 

 occipital, and its upper angles are not continued upon the sides of the foramen. 

 In the Chelonians the three elements of the occipital bone contribute to form the 

 condyle, as in Lizards and the Dicynodon ; but they project backwards from the 



^ * Plates III and IV. 



