198 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
parasphenoidal rostrum and wedged in between mesethmoid in front and the anterior, 
laterally compressed vertical plate of the basisphenoid just described. It extends 
upward and backward to the orbital plate of the frontal. From this region it sends 
outwards and backwards a pair of cartilaginous wings, which represent the orbito- 
sphenoids. 
The mesethmoid, in all but Apteryx, in common with the presphenoid region, forms 
a conspicuous interorbital septum. In the nestling Dromeus, Casuarius, Rhea, and 
?Ostrich, and in the adult Tinamou, this is pierced by a large interorbital fenestra. 
This fenestra appears to be excavated partly out of the large, backwardly directed 
plate which unites with the orbital plate of the frontal, and partly (caudad) out of the 
anterior border of the presphenoid. In the nestling, the antero-ventral border is more 
or less linguiform, and terminates at the level of the anterior border of the lachrymal. 
From this, there runs forward a narrow, triangular, cartilaginous septum nasi. In the 
adult Casuarius, Dromeus, Dinornithide, and 'Tinamous, ossification extends forwards 
almost to the end of the rostrum, and terminates in a vertical truncate border, beyond 
which there is a small cartilaginous septum nasi. In Rhea and Struthio the ossification 
extends quite to the free end of the rostrum, 7. ¢. relatively further forwards, and 
terminates in a sharp point instead of a vertical truncated border. In these, the 
cartilaginous septum nasi is wanting or greatly reduced. 
The dorsal border of the mesethmoid, in Dromeus, Caswarius, and Dinornithide, is 
of considerable thickness and very slightly convex; it forms a complete floor to the 
olfactory fossa, extending outwards on either side to the orbital plate of the frontal 
(Pl. XLIV. fig. 4). In this particular, as will be seen later, it differs conspicuously 
from Apteryx, wherein this region forms a thin median partition between two extensive 
cavities. At the anterior end of the olfactory fossa, both in Dromeus and Casuarius, 
it sends upwards, and then backwards, a strong median pillar deeply grooved on either 
side for the passage of the olfactory nerves. ‘This corresponds to the tegmen cranii 
described in Apterya by T. J. Parker, and referred by Kitchen Parker to the tegmen 
cranii of the lower vertebrates. Thus the erista gailli,in these two forms, is furnished 
entirely by this tegmen cranii, the “ tegminal process ” of Jeffery Parker. 
At the apex of this tegminal process, as has been well described by Parker, the 
mesethmoid reaches the outer surface of the skull; here it throws out lateral horizontal 
ecto-ethmoidal plates—the aliethmoids, as Jeffery Parker proposed to call them. In 
Dromeus the upper surface of these plates forms a lozenge-shaped area, bounded by 
the frontals behind, the nasals laterally, and the nasal process of the premaxilla in 
front. The free edges of these right aud left aliethmoidal plates in the nestlings turn 
downwards and inwards (Pl. XLIV. fig. 4), and in the adult become further extended 
and intricately folded to form the lower region of the aliethmoid and the antorbital 
plates. In the nestling Dromeus it should have been remarked that the median vertical 
portion of the mesethmoid is pierced by a large vacuity, the cranio-facial fissure. 
