PROFESSOR OWEN ON THE GENUS DINORNIS. 63 



for which latter bone it affords the major part of the glenoid cavity. The apophysary 

 part (8') 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. lig. 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 (o) 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 {t) 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 Une 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. As a 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. Pi. XXIV. fig. 6, exhibits in a remarkably perfect degree the three 

 transverse processes (4, s, 12) of the three principal vertebrse of the skull, together with 

 the basisphenoidal platform and the pterapophyses ( ' ) of the sphenoid. 



' I use this word instead of 'pterygoid processes," as the httter term has been emploped in Antbropotomy to 

 designate the independent bones which, in birds, articulate with the pterapophyses. 



