PROFESSOR OWEN ON THE GENUS DINORNIS. 63 
for which latter bone it affords the major part of the glenoid cavity. The apophysary 
part (s') of the mastoid descends vertically from its outer side for more than half an 
inch, external and posterior to the tympanic ; the inner side of the base of the process is 
perforated by the pneumatic foramen supplying air to the cancelli of the cranial walls. 
In consequence of the non-obliteration of the sutures in the young bird, to which this 
interesting cranial fragment has belonged, the right mastoid had become detached, ex- 
posing the great breadth of its suture with the parietal and alisphenoid ; and the pneu- 
matic foramen is exposed. The whole extent of the paroccipital process is preserved 
on this side. The loss of the frontals and orbitosphenoids from the fragment of skull 
in question shows the thickness of the cranial walls at the coronal suture (ib. fig. 3, r), 
and exposes the cranial cavity, which is here divided into epencephalic, mesencephalic, 
and prosencephalic chambers. The epencephalic division is entire, is excavated below 
for the medulla oblongata, and above for the cerebellum, and is perforated behind by 
the foramen magnum (fm). The mesencephalic division (0) consists of two small, 
well-defined, hemispheric pits for the optic lobes, in front of the lower part of the 
epencephalic chamber. ‘The portion of the prosencephalic division (p) above and ex- 
ternal to the depressions for the optic lobes is excavated in the alisphenoids and 
parietals: the thick cancellous walls form a striking contrast to the general character 
of the cranial parietes in birds. The deep subspherical sella turcica (¢) sinks down 
between the mesencephalic pits. 
As compared with the cranium of other birds, and particularly with those of the 
Ostrich and Emeu, the Dinornis and Palapteryx are remarkable for the forward produc- 
tion and lateral expansion of the upper cranial walls. In the Ostrich, a vertical line 
dropped from the point of union of the sagittal with the coronal sutures, would fall into 
the interspace between the basioccipital and basisphenoid: in the Emeu the same line 
falls behind the sella turcica; but in the Dinornis, the same line falls in advance of the 
sella turcica. In taking the greatest vertical diameter of the cranium of the Ostrich, 
the points of the compass touch the middle of the frontal region, and the interspace be- 
tween the pterapophyses’ of the sphenoid: the dimension is two inches five lines. In the 
Dinornis and Palapteryx, the lower point of the compass in this measurement touches 
the narrow presphenoidal prolongation of the sphenoid, and the dimension does not 
exceed two inches. Asa result of this anterior production of the frontal, it overhangs in 
a peculiar degree the coalesced prefrontals which are excavated to form the wide cham- 
bers of the olfactory capsules, and the upper walls of which chambers coalesce with the 
overarching part of the frontal. 
The cranium, Pl. XXIV. fig. 6, exhibits in a remarkably perfect degree the three 
transverse processes (4,8, 12) of the three principal vertebr of the skull, together with 
the basisphenoidal platform and the pterapophyses (’) of the sphenoid. 
1 T use this word instead of ‘pterygoid processes,’ as the latter term has been emploped in Anthropotomy to 
designate the independent bones which, in birds, articulate with the pterapophyses. 
