208 B. NATURAL HISTORY. 
tinuing round the temporal fossa, it sends forwards the usual zygo- 
matic arch, and — what is noteworthy — unites with both postfron- 
tal and malar, leaving the usual tripodal supplementary postorbital 
as a wedge-shaped plate, bounding the antero-inferior angle of the 
temporal fossa. The squamosal continues without interruption to 
the inferior extremity of the quadratum, concealing the latter 
entirely on a posterior view. I find no suture separating it from 
the superior portion already described, on either side of the cra- 
nium; and on reference to Owen’s figure of Ptychognathus 
declivis,* I find that he found them continuous in that species. 
He calls this element the “masto-tympanic,” which would be the 
Cuvierian nomenclature for opisthotic-quadrate of modern anato- 
mists. I find, however, that it does not include the quadrate 
which is situated immediately anterior to it, and does not appear 
to contain the opisthotic, which, as already described, is distinct. 
It is in fact figured by Owen in Pt. declivis, and named parietal, 
the close squamosal suture separating it from the posterior arches 
of the latter bone not having been detected. 
When the supposed quadrate bone is fractured, it is found to 
consist of two vertical plates, of which the anterior bears the nar- 
row transverse articular face for the mandible, excluding the poste- 
rior one. This I take to be the os quadratum. Its width is not so’ 
great as that of the posterior plate or squamogal, and it does not 
ascend much more than half way to the zygomatic arch. Its supe- 
rior margin appears to be received by the margin of the thicker 
superior portion of the squamosal, which somewhat overhangs it. 
I cannot trace its inner margin. A descending portion of the 
inner face of the squamosal approaches very near the posterior 
part of the pterygoid, and it is doubtful whether the quadratum 
extends interior to this point. The bony wall which appears 
below the prodtic has been already alluded to as continuous with 
the pterygoid expansion, but it may represent the lateral processes 
of the sphenoid, or even part of the alisphenoid. 
The squamosal or parietal sends down on each side a vertical 
plate, which terminates in a slender bony prolongation from its 
anterior margin. The plate is subquadrate, and twice as deep as 
wide antero-posteriorly. The osseous ethmovomerine septum ex- 
tends posteriorly to between the anterior margins of these lamine, 
and is prolonged inferiorly to the presphenoid, the suture with the 
latter extending beyond the anterior line of the above-mentioned 
* In Proceed. Geol. Soc., Lonid., xiv., Tab. 1. 
