Prof. Owen on the genus Dicynodon. 65 



(28) descending from the above attachments with a sigmoid curve in a vertical 

 direction, with a sHght incHnation forwards. They are relatively stronger than in 

 most Lizards, but are less robust and longer than in the Crocodilians or Chelonians, 

 in which the tympanic pedicles are wedged immoveably into the interspace of sur- 

 rounding bones, and in the Crocodiha extend obliquely downwards and backwards. 

 The position of the tympanic pedicles, and their comparatively free suspension, are 

 very characteristic of the Lacertian affinities of the Dicynodon. They terminate 

 below by a broad and slightly convex condyle, looking downwards and forwards, 

 for articulating with the lower jaw, and near this part receive abutments from the 

 par-occipital and sphenoid bones. 



The form of the temporal fossae (t, t) is a wide oval, with its long axis almost 

 parallel with that of the skull. The orbits (o, o) are large and almost circular, with 

 a complete bony frame or boundary. In the present species (D. lacerticeps) they 

 are relatively as large as in most Lizards, and larger than in the Crocodiles. Their 

 position, equidistant from both ends of the skull, is also a Lacertian character : in 

 the Crocodiles the orbits are nearer the back part, in the Chelonians they are 

 nearer the fore-part of the skull. 



The inter-orbital part of the surface of the skull is one-third broader than the 

 inter- temporal region, or true cranium, and gradually expands as it extends for- 

 wards. The contour of this part of the skull descends into the nasal region by a 

 gentle convex curve (fig. I.) : the surface is a little depressed along the middle, and 

 rises into a slight protuberance at the fore-part of the supra-orbital boundary, which 

 is formed by the pre-frontal (14). The mid- frontal (12) is divided by a median 

 suture, as in the Varanian Lizards and the Chelonia : it is a single bone in the 

 Crocodiles. In the Dicynodon, as in the Iguanas and American Monitors {Tho- 

 rictes, Tejus, &c.), the mid-frontal forms the middle two-thirds of the supra-orbital 

 ridge : the posterior part of this ridge and the upper half of the posterior rim of 

 the orbit are contributed by the post-frontal (11), which forms the medium of union 

 between the mid-frontal, parietal, malar and zygomatic bones. The malar (PI. III. 

 tig. 1 , 20a *) and superior maxillary bones (20) appear to be indistinguishably blended 

 together below the orbit, where they swell out in an unusual degree, and carry the 

 floor of the orbit much beyond the roof ; turning the aspect of the plane of the 

 orbit obliquely upwards and outwards, as in the Crocodiles, and rendering it less 

 vertical than in most Lizards. The fore-part of the orbit is bounded by the lachrymal 

 bone (16), which is extended upon the face, apparently as far as to the back part of 

 the nostril, in the present species. A single moderately large lachrymal foramen 



* The dotted angular line in front of 20 a indicates the position of the hollow base of the canine tusk, 

 not a suture. 



