8 MAEINE EEPT1LES OF THE OXFORD CLAY. 



The quadrate (q.) is a remarkably large and massively constructed bone. The body 

 is concave from side to side anteriorly and convex posteriorly. The posterior surface 

 is to a large extent concealed by the overlapping squamosal. The ventral end bears the 

 very large articular condyle, the form of which will be best understood from the 

 figure (PL I. fig. 1) ; it will be seen that the articular surface is divided by an oblique 

 ridge into a smaller postero-internal and a larger antero-external region. From the 

 inner border of the bone immediately above the condyle, it appears that a process 

 arose, which was overlapped by the posterior limb of the pterygoid. 



The parietals (par.) in their middle region form the high sagittal crest between the 

 very large temporal fossae ; posteriorly they widen and project considerably behind 

 the supraoccipital, with which they unite below. It is not quite clear to what extent 

 they were overlapped by the dorsal rami of the squamosals, but probably, as stated 

 above, these bones met in the middle line and formed the actual upper border of the 

 posterior face of the skull. 



Beneath the outer temporal crest the bones widen to form the roof of 

 the cranial cavity, and a little behind the pineal foramen they unite by their 

 lower borders with the upper ends of the columella? cranii (epipterygoids). In 

 front of this they widen and diverge to enclose the pineal foramen (p.f.), of which they 

 seem to form the whole margin, at least on the outer face of the skull. The relation 

 of the parietals to the frontals is obscure in the specimens examined : in the former 

 description it was stated that the two bones were probably anchylosed, but that there 

 seemed to be traces of a suture on the sides of the pineal foramen. Judging now 

 from the better-preserved skulls of Peloneustes (see p. 40) it seems probable that, 

 though the frontals may have extended back to the pineal opening on the inner side 

 of the skull, on the outer surface they are overlapped by a pre-pineal extension 

 of the parietals (Jr. in PI. I.) which meets the posterior ends of the facial processes of 

 the premaxilla?, thus excluding the frontals from the middle line, at least on the outer 

 surface of the skull. If this interpretation is correct, then the names of some of the 

 other elements of the skull-roof will be different from those given in the earlier 

 description and plate. At about the level of the pineal foramen the outer edge of the 

 parietal unites with an element which must be the postfrontal (po.f.). In front of this is 

 another element which helps to form the upper edge of the orbit ; this was regarded 

 as a prefrontal and is marked pr.f. in PL I., but probably it is the outer part of 

 the frontal which, judging from the skull of Peloneustes, meets or nearly meets its 

 fellow in the middle line beneath the parietals and extends back to the pineal 

 foramen. The true prefrontal is probably the bone marked 1s.07'b. and \n. in PL I. ; 

 it extends forwards to meet the maxilla and is produced anteriorly into a narrow 

 process, forming the inner border of the external narial opening : it is possible that 

 a nasal element is represented by this part of the bone, but no suture is visible. 



The anterior portion of the orbital border is formed by an element separated from 



