186 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
From its dorsal surface in Dinornis there arises a large hollow shell of bone, the inner 
wall of which embraces the triangular plate of the rostrum. The cavity of this bony 
shell—the antrum—opens posteriorly by a large foramen into the quadrato-jugal fossa. 
It articulates with the palatine by a short recurrent process from its postero-internal 
angle. 
In Emeus there is no antrum. What corresponds to its inner wall in Dinornis exists 
as a flat concavo-convex vertical plate applied to the anterior border of the mesethmoid 
triangular process and the rostrum. 
In Rhea the maxilla is almost entirely represented by the maxillo-palatine process. 
Viewed dorsally it is seen to take the form of a flat, triangular, perforate plate of bone, 
with its sharply pointed end running forwards to within a short distance of the 
anterior end of the external narial aperture. ‘This more pointed region rests upon the 
palatine process, and is bounded externally by the maxillary process of the premaxilla. 
Its postero-mesial border is bounded by the vomer. Its hinder end presents free 
postero-internal and external borders. The former lies more or less markedly forward 
than the latter, and bounds the posterior nares anteriorly. ‘The latter lies more or less 
considerably caudad, and bounds the anterior end of the quadrato-jugal fossa. Its 
postero-internal angle is produced backwards into a long spine, which is closely 
applied to the outer border of the palatine, extending backwards for a considerable 
distance. Its postero-external border is also produced backwards spine-wise, and 
underlies the quadrato-jugal bar. From the dorsal surface of the maxillo-palatine 
plate there arises a long slender style which, directed upwards and backwards, ultimately 
articulates with the anterior angle of the lachrymal, and thus serves to divide the 
lachrymo-nasal (antorbital) from the nasal fossa (Pl. XLIII. fig. 9). In all other 
birds this is done by the descending maxillary process of the nasal. The antrum is 
represented only by a minute aperture at the base of the vertical rod—the lachrymo- 
nasal process of the maxillo-palatine—just described. 
The guadrato-jugal fossa extends forwards nearly as far as the level of the anterior 
end of the posterior nares. 
In Struthio the maxilla is splint-shaped, produced posteriorly into two spine-like 
processes, the inner of which runs dorsad over the distal end of the palatine, the outer 
running ventrally below the quadrato-jugal bar. Anteriorly it extends forwards 
nearly as far as the body of the premaxilla. The maxillo-palatine processes are small 
and hatchet-shaped ; their mesial borders clamp the vomer, which is grooved laterally 
for their reception. ‘There is a small shallow autrum, the roof of which is fenestrated. 
The anterior border of the maxillo-palatine process bounds the enormous palatine 
foramen posteriorly. 
The ossified style, described in Rhea as dividing the lachrymo-nasal from the nasal 
fossa, is here represented by a ligament springing from the external dorsal angle of the 
mouth of the antrum and inserted into the short descending process of the nasal. 
