AND CLASSIFICATION OF THE FOSSIL REPTILIA. 
245 
usually developed backward somewhat further. The condyle is less prominent than 
in Chelonians. Above it is the foramen magnum, more or less extended vertically, 
with sub-parallel sides. The occipital plate consists of the usual four occipital 
elements, though the sutures between them may become obliterated. They are at 
first well defined, but much closer than the sutures which connect the occipital plate 
with the bones which occur above it and at its sides. The supra-occipital forms the 
upper part of the foramen magnum, the ex-occipitals make the lower parts of its 
sides, and the basi-occipital is below. The sutures between this bone and the ex- 
occipitals run down the descending processes which have been termed hypapophyses. 
A large bone is situate above the supra-occipital, and extends the occipital plate 
vertically. It has an immense anterior extension, may apparently be single or double, 
enters into the brain-case, and I identify it as the inter-parietal, and regard it as 
homologous with the bone so named in Mammals and Lizards. 
At the sides of the occipital plate are the large squamosals, elongated vertically 
and expanded laterally. Their connection is mainly with the ex-occipital bones. It 
is their reflection backward which forms the basin-shaped occipital surface found in 
Dicynodon 2 mrd{ceps and other types. It is this bone which furnishes the Mammal¬ 
like zygomatic process from its anterior border, and it supports the quadrate bone on 
its base. 
Two other bones are found at the back of the head, which form a pair, and lie 
between the inter-parietal, supra-occipital, and squamosal. They are, apparently, thin 
plates, which correspond with the similarly placed bones in Labyrinthodonts, which 
have been termed epi-otic bones. 
Between the ex-occipital and the squamosal is a large foramen, which may be 
auditory ; and at the sides of the ex-occipital elements of the condyle are foramina, 
which may be outlets for the vagus nerve. 
There is no certain evidence of the basi-occipital being divisible by suture from the 
basi-sphenoid, but such a separation is probable (although a vertical section fails to 
show it), because the hypapophyses which are prolonged downward from the region 
of these bones sometimes show at their termination a tri-radiate groove, and it has 
been seen that the basi-occipital and ex-occipital contribute the posterior two of these 
three elements.' 
These sphenoido-occipital processes form, at their outer lateral termination on each 
side of the head, a remarkable crescentic concave articulation. A small bone 
articulates with it and extends to the squamosal, near to the quadrate or to the 
quadrate bone. The bone may be very small and sub-quadrate in form, or sub- 
cylindrical and constricted a little in the middle, with convex articular ends. These 
bones are much smaller than the pear-shaped bones in Ichthyosaurus, which have a 
large lateral attachment at the junction of the basi-occipital and basi-sphenoid, and 
which extend transversely outward, so that the small end is received into a pit in the 
quadrate bone, and they are much less slender than the bones which in some Liassic 
