200 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
angular. It furnishes the articular surface for the quadrate. In Dromeus and Apteryz, 
both angular and supra-angular take part in the protection of its external face. 
The stapes is represented in the dried skull only by the bony base. It does not 
apparently offer any characters of value from a systematic point of view. The extra- 
columella has been already admirably described by Gadow, Parker, and others. 
The Membrane-bones. 
The parietal, in Casuarius, Dromeus, and ? Struthio, is a transversely oblong plate 
of bone, the anterior and outer borders of which are produced forward into a small 
but sharp point which is wedged in between that portion of the frontal which over- 
hangs the post-orbital process and the process itself. This parietal spur thus helps to 
form the base of the post-orbital process, the main body of which is furnished by the 
alisphenoid. 
In Rhea and t Tinamous this antero-external parietal angle is not produced forwards, 
and fails entirely to reach the postorbital process (Pl. XLIII. fig. 9). Its postero- 
external angle is overlapped by an upstanding process of the squamosal. 
Internally the parietal carries on the tentorial ridge from the alisphenoid upwards to 
its junction with the falx. Behind this ridge it is gently scooped out to complete the 
roof of the cerebellar fossa, in front it is also hollowed out to form the posterior wall 
of the cerebral fossa. 
In Apteryx, as in the other forms, the parietal is irregularly four-sided. Its external 
border is bounded entirely by the squamosal. In all the other forms, it will be noted, 
it extends forward beyond this. 
Internally, it is found to lack the tentorial ridge. Its hinder and external borders 
pass insensibly the one into the other. ‘The former skirts the supra-occipital and a 
portion of the pro-6tic beyond, the latter rises gently from the hinder region of the 
superior border of the pro-6tic—where the hinder border may be said to cease—upwards 
to skirt the upper border of the small triangular area of the squamosal which enters 
into the formation of the inner wall of the skull. It is entirely cut off from the 
alisphenoid. In the other forms, e. g. Rhea, Dromeus, the superior borders of the 
pro-dtic and the alisphenoid form the boundaries ventrad of this bone. 
The frontal extends backwards so as to form the greater part of the roof of the 
cerebral fossa. Its hinder border is more or less sinuously curved, and traced from 
within outwards will be found, in Casuarius and Dromeus, to run transversely from the 
middle line to the base of the post-orbital process, from which, however, it is actually 
cut off by a very slender spur from the parietal. In Rhea, on reaching the antero- 
external angle of the parietal, it turns abruptly upwards and outwards, so as to rest 
upon the base of the post-orbital process itself. Externally, the frontal is bent in upon 
itself to form a deep orbital plate which articulates caudad with the alisphenoid and 
cephalad with the mesethmoid, eventually terminating in a long spike, in hea, resting 
upon the mesethmoid, and overlapped by a greatly elongated posterior extension of the 
