PHYLOGENY OF THE PALZOGNATHA AND NEOGNATH A, 177 
In many Dinornithide these apertures lie closely packed together down the mouth 
of a deep lacerate fossa. 
In most of the other Palwognathe more or fewer of these foramina become more 
or less confluent one with another and with the optic foramen. 
The Ethmoidal Region.—The mesethmoid, in all but Dinornithide and Apterys, 
forms the thin median septum known as the interorbital septum. It is continued 
forward into the pre-lachrymal fossa as far as the cartilaginous septum nasi. Its 
ventral border rests upon the parasphenoidal rostrum ; its dorsal border affords support 
to the frontal and nasals. ‘This it does by means of paired, lateral, horizontal, ecto- 
ethmoidal plates. These, the superior aliethmoids, curve outwards and downwards, 
as the inferior aliethmoids, to form the walls of the olfactory chamber. It is 
perforated superiorly in the dried skull so as to place the two olfactory chambers in 
communication in all but Apteryx, Casuarius, and Crypturi. 
In Dromeus and Casuarius the whole of the outer wall of the aliethmoidal region— 
the only region that ossifies—is deeply invaginated. The lower region of this in- 
vaginated wall forms a large, outstanding, antorbital plate, to the outer free edge of 
which the lachrymal is closely applied (Pl. XLIV. fig. 1a). The olfactory chamber is 
thus reduced to a narrow slit-like cavity, whose outer wall is scroll-shaped, the scroll 
being formed by the invagination before mentioned. 
This invagination lodges the Harderian gland, and is called therefore the Harderian 
fossa. Opening above and behind this is a small supra-orbital fenestra. 
In Rhea the invagination of the aliethmoidal wall is less sharply marked, and the 
Harderian fossa, though larger, passes gently backward into the orbit. Except in 
very old specimens, the greater portion of the wall of this fossa remains unossified. 
The supra-orbital fenestra, when ossification is complete, is large. 
In Struthio only the superior aliethmoidal wall is ossified. The postero-inferior 
region forms the antorbital plate; this is continued upwards and forwards to form 
the roof of the olfactory chamber. ‘There is a supra-orbital fenestra. 
In Crypturi the antorbital plate stands out at right angles to the mesethmoid as 
a narrow bar of bone. ‘The upper portion of the aliethmoidal wall resembles that 
of Rhea in being deeply invaginated, so much so as to force it inwards almost on to 
‘he mesethmoid, thus forming a huge Harderian fossa and reducing the olfactory 
chamber to the smallest possible limits. ‘There is a well-marked supra-orbital fenestra. 
In all the Palwognathe, save the Crypturi, the ossified ectoethmoidal plate extends 
backwards, on either side of the dorsal border of the interorbital septum, as far as the 
brain-case. ‘Thus only the lower region of this septum is visible in the skeleton, not 
its whole extent as in Neognathe. ‘This feature is most noticeable in the Dinornithide 
and in Apteryx. In these the olfactory chambers are of enormous size, extending 
backwards nearly or quite as far as the optic foramina, thus so far encroaching 
upon the orbit as to obliterate the interorbital septum. ‘This last is traceable only 
