of the Skull in Peloneustes philarchus. 253 
facial processes of the premaxille, while laterally they are 
bordered by the prefrontals in front, and probably for a short 
distance only by the postfrontals behind. 
The inner border of the postfrontal united with the 
parietals; its anterior boundary is not seen in any of the 
specimens, but it probably met the prefrontal in a suture 
running outwards nearly at right angles to the axis of the 
skull, as in the above-mentioned skull of Pliosaurus. It 
evidently formed part of the upper posterior margin of the 
orbit and of the anterior border of the temporal fossee. Its 
lower extremity apparently united with the postorbital. The 
relations of this bone to the surrounding structures, apart 
from its anterior junction with the prefrontal, are very similar 
to those of the postfrontal of Sphenodon. 
The prefrontal is bounded internally by the frontal and 
posterior end of the premaxille ; posteriorly, as has just been 
mentioned, it is probably in contact with the postfrontal ; 
anteriorly it joins the nasals(?), and externally it is slightly 
overlapped by a thin plate of bone, here regarded as a supra- 
orbital, the presence of which in a skull of Plestosaurus 
dolichodirus was long ago pointed out by Owen *. 
It has not been possible to determine the form and rela- 
tions of the nasals, but they seem to have sent forward a 
wedge-shaped process forming the greater portion of the inner 
margin of the nostrils, and separating them from the facial 
processes ¢ of the premaxille. I cannot say whether a 
lachrymal was present or not. The probable structure of this 
part of the skull is shown in woodcut 2 A. 
The relations of the bones of the frontal and nasal regions 
of the skull are much better shown in the skull of Phosaurus, 
to which frequent reference has already been made. 
The lower border of the orbit is formed in great part by 
the jugal (woodcut 2B). This bone is supported below by the 
backward prolongation of the maxilla, which extends consider- 
ably behind the orbit ; its hinder portion unites above with the 
postorbital, and posteriorly it joins the anterior ramus of the 
squamosal, but takes no share in the formation of the upper 
margin of the temporal bar, being excluded therefrom by the 
backward extension of the postorbital to meet the squamosal. 
The postorbital is a triangular bone; its apex must have 
joined the postfrontal, but in no specimen is the actual 
junction preserved, though there can be no doubt that it 
* “Rept. Lias Form.,” pt. 3 (Mon. Pal. Soc. 1865) p. 9, pl. ii1. fig. 1. 
+ The upper portions of these processes were described as the nasals by 
Owen, Sollas, and others. 
Ann. & Mag. N. Hist. Ser. 6. Vol. xvi. 18 
