Prof. Owen on Dicynodon tigriceps. 235 



surface is 13 inches ; the height of the same surface from the end of the basi- 

 occipital processes is 8 inches. 



The occipital condyle (PI. XXXI. i), which was broken away in the previously 

 described specimens*, is entire in one of the large skulls, and in a fragment of 

 another now under description : it is single, convex, subpedunculate, projecting 

 freely from the foramen magnum with a broad reniform contour, being slightly 

 excavated above : it seems to be formed wholly by the basioccipital, and appears 

 small in proportion to the entire skull, the attachment of which to the trunk must 

 have been powerfully secured by the mass of muscles inserted into the spacious 

 and well-ossified occipital region {ibid. 3, s, 4). The transverse diameter of the con- 

 dyle is 1 inch 10 lines, its vertical diameter 1 inch 4 lines : on each side of the 

 upper part of its base is the foramen condyloideum : the foramen magnum is a 

 vertical ellipse, 1 inch 8 lines in its long diameter, and 10 lines across. 



The basioccipital sends downwards a pair of hypapophyses (hy), which slightly 

 diverge as they descend : they are subcylindrical, straight, truncated, 1 inch 9 lines 

 in length, 1 inch in breadth, and deeply excavated externally, as in the IguaneB 

 and some other Lizards. From the outside of the base of this process the (par- ?) 

 occipital extends outwards, downwards, and backwards, terminating in a low and 

 large obtuse process (4), projecting backward, close to where this part of the occi- 

 pital seems to unite with the tympanic. 



The ex- and super-occipitals form a large triangular expanse of bone (3), vertical 

 in position, but undulated and concave laterally above the foramen magnum, where 

 it inclines a little forwards as it ascends : this expanse is overarched by the parieto- 

 mastoid ridges (?> s) on each side, where the surface is slightly convex at its upper 

 half, concave below. 



The major part of this peculiarly expanded occipital bony surface is formed of a 

 comparatively thin subvertical plate of bone, formed by the branch of the parietal, 

 the mastoid, and contiguous parts of the occipital : which plate afforded attachment 

 at its posterior surface for the nuchal muscles, at its anterior one for the temporal 

 muscles. 



The cranium proper has the usual reptilian contracted calibre, and it seems the 

 more contracted in the present great Dicynodon by comparison with the extent of the 

 occiput and the still wider expanse and span of the zygomatic arches on each side. 

 The upper surface of the cranium (PI. XXIX.) is almost flat ; it is horizontal, and 

 is bent forwards at nearly a right angle with the occipital surface. It is bounded 

 on each side by the temporal ridges, which turn the convexity of their curve towards 

 each other: there is an eminence perforated by the foramen parietale (?)! in the 



* See Pis. iii.-vi. 



f The foramen parietale has its margin raised in old and large Iguanas. 



