210 DR. EMBLETON AND ME. ATTHEY ON" THE 



border of the same bones, by the malars, quadrate jugals, and 

 quadrate bones. 



The inferior surface of another skull in Mr. Atthey's collec- 

 tion is shown, of natural size, in Plate III., fig. 1. The poste- 

 rior 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 maxil- 

 lary 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 Arcliegosaurus, are called by Yon Meyer, in his work 

 before quoted, " supraoccipitals." Immediately below this bor- 

 der 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 articulate 

 next the median line with the supraoccipital and then with the 

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

 toids; their lower borders, external to the foramen magnum, 

 rest upon the basioccipital, and have on each a projection poste- 

 riorly, 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 



