200 ME. W. P. PYCKAET ON THE MOEPHOLOGT AND 



angular. It furnishes the articular surface for the quadrate. In Dromceus and Apteryx, 

 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, Dromceus, and IStruthio, 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 ITinamous this antero-externa.1 parietal angle is not produced forwards, 

 and fails entirely to reach the postorbital process (PI. XLI1I. 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-otic beyond, the latter rises gently from the hinder region of the 

 superior border of the pro-otic — 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, Dromceus, the superior borders of the 

 pro-otic 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 Dromceus, 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 aud 

 cephalad with the mesethmoid, eventually terminating in a long spike, in Rhea, resting 

 upon the mesethmoid, and overlapped by a greatly elongated posterior extension of the 



