ZOOLOGY. 201 
no line of division to be discovered.* It will be seen later that the 
same structure exists in the Anomodontia and Sphenodon. It is 
not impossible that its anterior portion will be found to represent 
the element in Teleostei, ealled by Huxley, perhaps by error, 
Squamosal. 
Returning to the external arches, we find the zygomatic is par- 
tially vertical, owing to the large size of the orbit and the shortness 
of the posterior region of the cranium, and that it is extended by 
a supernumerary bone not found in the Mammalia, for which I 
adopt the name given by Owen in this genus, of postorbital. (Figs. 
2, 4,13, Pob.) It is the temporal of the Testudinata of Cuvier, 
and one of the postfrontals of the Lacertilia of the same author. 
It is most erroneously called quadratojugal by Stannius, and by 
Giinther, who follows him, in Sphenodon. 
Anteriorly it articulates with the malar, here a long slender bone 
on account of the size of the orbit, and which, as usual, articulates 
anteriorly with the maxillary. Posteriorly the extent of the post- 
orbital separates it from the squamosal, as is the case with some 
Lacertilia; while a short quadratojugal connects it with the quad- 
ratum, precisely as in the Crocodilia. This latter bone is the squa- 
mosal of Owen, who, on account of this erroneous determination, 
was compelled to apply a new name to the true squamosal, calling 
it “supratemporal.” (See Paleontology, p. 198.) 
Posterior to the postfrontal and postorbital, is an ovate bone 
connecting them with the squamosal. This is also peculiar to this 
order, and is the supersquamosal of Owen. 
The postorbital arch is quite horizontal, and is composed of the 
postfrontal exclusively. 
Turning to the superior aspect of the cranium, if we assume 
that the two posterior elements bounding the temporal fosse are 
continuous with the squamosal, as has been above shown, there is 
no difficulty in determining the elements in front of them. Thus 
the undivided bone with large fontanelle near the posterior margin, 
bounding the squamosals anteriorly, would be the parietal. The 
posterior half of each of these bones is concealed by the anterior 
portion of the laminar squamosal as in Sphenodon: they descend 
beneath the latter to a point a little before the line of the middle 
of the temporal fossa. It scarcely touches its fellow on the median 
line behind the fontanelle. The general shape of the bone is 
* I have since found a suture in two of our Ichthyosaurus crania, and Dr. 
Seeley states that that is the normal structure. 
A.A. A.S. VOL. XIX. 26 
