222 PROF. H. G. SEELEY ON THE [Mar. 21, 



Quadrato-sqiiamosal Arch. — The squamosal bone, which occupies 

 a small area on the lateral aspect of the skull between the post- 

 squamosal above and the quadrate bone below, is better seen on 

 the occipital aspect (text-fig. 32), where it forms the upper and 

 narrower part of the quadrato-squamosal pedicle for articulation 

 with the mandible. The pedicle is nearly vertical, being inclined 

 slightly backward as it extends downward , is convex on the straight 

 side, and concave on the outer part, where the portion regarded 

 hitherto as the quadrato-jugal is prolonged behind this surface out- 

 ward and backward. The posterior aspect of the pedicle is crossed 

 obliquely in its middle part by the sagittate suture which divides 

 the squamosal bone from the qiiadrate, so that, passing downward 

 and inward, it does not reach the mandibular articulation, which 

 is formed by the quadrate bone. The height to the roof of the 

 skull is Jo iiich. The transverse width of the quadrate bone at 

 the articulation is about half an inch. This is exclusive of the 

 great internal jDrocess of quadrate contour which extends inward 

 and forward above the infra-quadrate process of the pterygoid 

 bone, and internal to the descending process of the squamosal, and 

 is exposed in one skull by removing the occipital bones. 



The occipital surface of the skull, properly so called, is entirely 

 behind the squamoso-quadrate region. Its vertical measurement 

 is about half an inch, and the transverse width about an inch and 

 a quarter. Below the postsquamosal bones its contour inclines 

 to be transversely fusiform, owing to the inferior median basi- 

 occipital convexity and the lateial concave infeiior emargination 

 below the opisthotic bones (text-fig. 32). 



The foramen magnum occupies the middle of the area. It is 

 higher than wide, wider below than above, margined laterally by 

 an elevated rounded border, such as might possibly have carried 

 a pro-atlas. Inferiorly this border merges in the occipital condyles, 

 which are defined by a median concavity. The sutures are not 

 distinct, but the basioccipital appears to enter into this median 

 concavity, so that the two condyles from which the bony tissue 

 has been rubbed are upon the exoccipital bones. Above the 

 condyles a transverse horizontal suture separates the exoccipital 

 from the supraoccipital bones, which are lai^ger. Externally 

 these bones are limited by a vertical suture, which separates them 

 from the opisthotic, which is subtriangulai- and terminates outward 

 in a blunt process below the postsquamosal and slightly in advance 

 of it. There may be an interparietal above the supraoccipital 

 bones and below the parietal. The flattened surfaces of these 

 bones appear a little concave, owing to the elevation of the border 

 of the foramen magnum. The distinctive character of this 

 region is the closed occiput, which is more like that of Crocodilus 

 than Testudo, and if the quadrate bones of a Crocodile were 

 directed downward instead of backward, the occipital region of the 

 skull would be more closely comparable with. Frocolophon in its back- 

 ward extension and elevation above the mandibular articulation. 

 The only South African reptile which approximates to this 



