50 Messrs. Embleton and Atthey on the 



lection is shown, of natural size, in Plate VI. fig. 1. The 

 posterior part only is given. 



III. The Occipital Surface. — It is impossible to estimate the 

 height of the occiput, owing to the crushing it has undergone ; 

 it is much flattened, concave on the whole from side to side 

 (that is, from the posterior external angle of one mastoid to that 

 of the other) ; external to the occiput project backwards and 

 outwards on each side the posterior lateral angles of the 

 maxillary part of the cranium. 



The upper border of the occipital surface is also the posterior 

 border of the middle part of the skull, and overhangs slightly 

 the parts beneath it. It is formed externally by the mastoids 

 and between them by the pair of bones corresponding to those 

 which, in Archegosaurus, are called by Von Meyer, in his 

 work before quoted, " supraoccipitals." Immediately below 

 this border runs a transverse line of suture connecting the 

 bones forming the border with those beneath it — namely, next 

 the median line with the single and, as we deem it, the true 

 supraoccipital, and laterally with the exoccipitals. 



The supraoccipital is of a subtriangular form, wider from 

 side to side than from above downwards, and situated on the 

 median line. It is doubtful whether or not the median suture 

 passes through it. Below it articulates with the exoccipitals. 



The exoccipitals are a pair united by suture on the median 

 line below the supraoccipital ; they form the upper portion 

 and sides of the foramen magnum ; their upper borders arti- 

 culate next the median line with the supraoccipital and then 

 with the supraoccipitals of Von Meyer, and further out with the 

 mastoids ; their lower borders, external to the foramen mag- 

 num, rest upon the basioccipital, and have on each a projec- 

 tion posteriorly, terminated at its inner side by a flat rounded 

 articular facet looking backwards, for articulation, doubtless, 

 with the neural arch of the atlas. Between these facets is a 

 notch, the uppermost part of the foramen magnum ; the lowest 

 part of the foramen is the upper edge of the cotyloid cavity of 

 the basioccipital. Owing to the compression of the skull, the 

 foramen, however, is not easily made out. 



External to the facets there is on each side a rather pointed 

 process, apparently for muscular attachment; and beyond these 

 again, at a short distance, are the tooth-like processes of the 

 underside of the mastoids, mentioned in the description of the 

 upper surface of the skull. 



Below these parts is the inferior surface of the skull, 

 described in section II. 



IV. The Mandible (Plate VI. figs. 2 &3).— Two half-man- 

 dibles, right and left, occurred, as is stated at the commence- 



