PHYLOGENY OF THE PALAOGNATHA AND NEOGNATH. 181 
In Apteryx it appears to be reduced to the vanishing point. It is extremely small, 
oblong in shape—its long axis horizontal,—and more or less sharply defined, when 
seen at its best. It lies entirely behind the level of the pituitary fossa. It is 
bounded above by a low tentorial ridge, in front by a ridge of bone dividing it from the 
pituitary fossa, below by the rim of the metencephalic fossa, and behind by a huge 
projecting shelf-like ledge from the tentorial ridge, The trigeminal foramen opens at 
its postero-dorsal border, the orbito-nasal in its anterior border. 
In A. haasti the outer wall of this fossa is almost entirely absorbed by a large aperture 
common to the trigeminal and orbito-nasal nerves. 
The pituitary fossa in Casuarius is a deep pocket-shaped depression. Its mouth is 
directed slightly forwards. The rim thereof forms the dorsum selle behind, and the 
pre-pituitary ridge in front. Within the mouth of this fossa (Dinornis) or on its rim 
(Dromeus) is the oculo-motor (1t.) foramen. The pathetic (1v.) foramen lies above and 
to the outer side of the oculo-motor, ofien it serves also for the passage of the internal 
ophthalmic artery. Anterior to the prepituitary ridge in the middle line is a narrow 
knife-like optic platform, on either side of which are the confluent optic foramina. 
The optic platform is continued upwards vertically and again expands to form the 
pre-optic ridge, which in Dromeus, and slightly less obviously so in Caswarius, joins 
the tentorial ridge. 
In Struthio the pituitary fossa is of great depth; the pre-pituitary ridge and optic 
platform are well marked. 
In Dinornithide the fossa is comparatively shallow, but of considerable circumference. 
The optic platform is very wide. 
In Apteryx the pre-pituitary ridge is but feebly developed. ‘The optic platform is 
not distinguishable from the pre-pituitary ridge, which divides the optic foramina one 
from another, ‘The pre-optic ridge is well developed and overhangs the fossa, the 
mouth of which, in consequence, has a semicircular outline. It should be mentioned 
here that the bottom of the fossa is produced forwards into a yet deeper, almost 
spherical, depression, overhung by the pre-pituitary ridge. 
In Tinamous this fossa is deep and tubular in form. 
The cerebral fosse are sharply defined in all the Palwognathe save Apteryx. In all, 
with the exception just mentioned, the cerebral lies entirely in front of the cerebellar 
fossa. In Apteryx, and to a lesser extent in the Crypturi, the cerebellar contour is 
scarcely distinguishable from the cerebral. The tentorial ridge, which serves to cut off 
the cerebral from the remaining fosse, arises from the level of the pre-optic ridge and 
trends outwards and backwards to the level of the top of the pro-étic; from this point 
it turns sharply upwards and forwards to meet in the mid-dorsal line, over the region 
corresponding with a vertical line passing upwards from the dorsum selle. That 
portion of the ridge which forms the upper boundary of the mesencephalic fossa in 
Casuarius and Dromaus is of great depth, and projects into the cranial cavity like a 
VoL. xv.—Part vy. No. 10.— December, 1900. 2D 
