Osteology of Palaeornis. 
587 
on the dorsal aspect of the bone, while practically found in the same 
localities, are far more numerous and more abundant. These foramina are 
almost entirely absent in the sternum of my specimen of Ara severa, and on 
the right-hand side of the same bone the elliptical xiphoidal foramen, 
although completely closed in posteriorly, the postero- mesial angle of the 
outer portion is merely in contact with the postero-external angle of the mid- 
xiphoidal portion. On the left-hand side the hinder margin of the foramen 
is entire, with a width of a little more than a millimetre. 
Sometimes the xiphoidal foramina are entirely closed in, and this is the 
case in the sternum of a skeleton of Cacatua leadheateri in my collection. 
On the dorsal aspect of this sternum, anteriorly, there is formed, mesially, a 
stout bridge of bone, extending backward from the middle point of the 
anterior border to a point in the middle line some five or six millimetres 
posterior to it. Beneath this are found pneumatic foramina, and nowhere 
else in the bone, apparently. A bridge corresponding to this, only rather 
shorter, is also found in a sternum of Amazoua leucocephala, with a circular 
pneumatic foramen on either side of it. This parrot, too, may have either 
one or both of the large xiphoidal foramina closed in posteriorly in the same 
manner as I have just described for a case as found in Ara severa ; while in 
addition to this I find here, on either side, a small, circular foramen, situated 
between the big elliptical one and the keel close to the hinder border of the 
bone. This bone, however, is often subject to decided variation in species 
belonging to the same genus ; and I find in a sternum of a specimen of 
Amazona oratrix in my collection the aforesaid bridge entirely absent, only 
one pair of small, irregularly outlined xiphoidal foramina present, while on 
the dorsal aspect there is a line of minute pneumatic foramina occurring 
down half the middle line anteriorly, with a few scattered ones behind the 
anterior border, chiefly near the thickened central portion. 
Mivart found, in a specimen of Lorius flavojjalliatus, the sternum having 
two — one large and one small — xiphoidal foramina on the right side and 
none on the left. So it goes ; and I believe, when such variations as these 
are present, there is no hard and fast rule for the presence or absence of 
these vacuities in the sternums of the Psittaci, even in the same species. 
The Pectoral Limh. — Considerable variation is found here with respect 
to the pneumaticity of the bones of this part of the skeleton. In Palaeornis 
docilis only the humerus appears to enjoy this condition, and this is likewise 
the case in Amazona oratrix and Amazona leucocejphala, in Ara sevtra, and 
such cockatoos as I have examined, while in Ara chlorojjtera the entire 
skeleton of this limb appears to be more or less pneumatic. 
Eeturning to Palaeornis docilis, it is to be observed that the humerus has 
a straight, comparatively short shaft, which exhibits some transverse 
flattening. The radial crest is conspicuous though short, and bluntly 
pointed, while it is bent downward and outward towards the palmar aspect 
