Osteology of Palaeornis. 
581 
of Ara cMoroptera at hand, that no line of sutural union is visible, while the 
anterior portion of the process has conformed itself entirely to the form of 
the encircling bone. I am inclined to believe, however, that, as in Palaeornis, 
the lacrymal hone here, too, extended backward to meet the post-frontal 
apophysis, rather than the latter extended forward to meet the lacrymal. 
Now, in Amazona leucocephala the lacrymal bone a^ain completes the circlet, 
meeting and fusing with the anterior end of the joost-frontal process ; but as 
it passes the apex of the squamosal process below, it develops a slight 
elevation on its lower edge, which is directed toward the apex of the squamosal 
process as though it were making an effort to reach it. 
In the cockatoos (Cacatua leadheateri) this imion is not only accom- 
plished, but it is so extensive that a bony plate is formed in this locality, 
stretching between and fusing with the two lateral processes of the side of 
the cranium — that is, the post-frontal and squamosal apophyses — to such an 
extent that a large foramen exists between them, into which leads the 
crotaphyte fossa of the same side of the skull. As the crotaphyte fossa 
harbours the temporal muscle, the tendon of which is inserted into the 
mandible,* this plate forms a very effective osseous protection to that 
muscle, for which there seems to be no sufficient reason apparent. 
Thus we see that the encirclature of the orbit in parrots differs 
considerably in the different genera ; but this in no way explains why these 
birds should require that their orbits be entirely surrounded by bone and as 
extensively so as in the big macaws. That there is some reason for it there 
can be no doubt, or else the lacrymal bone would not take upon itself such 
a supreme effort to form that osseous surrounding ring through reaching to 
the apex of one of the lateral processes of the cranium in one series of forms, 
and to the apex of the other process in all other parrots, apart from 
Palaeornis, in so far as I know, including the Owl Parrot (Stringops). 
The mandible of Palaeornis docilis (Plate XL, figs. 4 and 5) lias the 
usual broad U-shaped form found in the case of this bone among parrots 
generally, and, as is always the case, it is highly pneumatic. Beyond the 
articular extremities its upper, free margin is thin and sharp ail the way 
round. Relatively speaking, its symphysis is not as deep as it is in the 
macaws {Ara) or in many other parrots. Viewed directly from the front, 
its free dentary margin forms in outline another U, the open part being 
above. The lower ramal border is slightly thickened, while the articular 
ends are truncated above in the downward direction from before backwards. 
Here each shows the peculiar, shallow, antero-posterior facet for articulation 
with the quadraie of either side. On the upper aspect, posterior to either 
one of these, is a large, pneumatic foramen, and occasionally a smaller 
opening of the kind exists in front of it. In Ara chloroptera the mesial 
* Shufeldt, R. W. : " Myology of the Eaven/' London, 1901, p. 28, fig. 7, and 
other figures. 
40 
