36 
Philippine Journal of Science 
1919 
less protected by the conformation of the quadrate when that 
element, upon either side, is placed in articulation. 
There are some twelve to fifteen sclerotal plates to the circlet 
in either eyeball; the smaller ones are situated anteriorly and 
the larger ones behind (Plate III, fig. 9). Each platelet is an 
irregular quadrilateral in outline, the whole arrangement being 
fitted to the requirements of the form of the external moiety of 
the globe, assisting very materially in protecting it from certain 
injuries, and maintaining the sphericity of the organ. Addi- 
tional strength is afforded through the generous overlapping 
of the plates. 
We find the characters presented on the part of the mandible 
among the eagles pretty much the same, and it is V-shaped in 
all of the species at hand. In the long-faced species the V is 
more elongate, and the angle formed by the rami more acute. 
The bone is more or less pneumatic, which is also true of the 
cranium as a whole. In Pithecophaga a side of the mandible 
has a length of 9.7 centimeters, and the symphysis 2.5 centi- 
meters, the latter being concave transversely above and corres- 
pondingly convex on its ventral aspect. All the elements are very 
solidly fused together, with the superior and inferior borders 
rounded. There are no perforating vacuities anywhere, the 
entire bone being very strong and smooth. A low coracoid pro- 
cess is present on either side, and from either of them the 
superior border slopes rather abruptly downward to the articular 
enlargement of the same side (Plate I, fig. 1; Plate III, fig. 4). 
Posteriorly, an articular extremity is considerably compressed 
from above downward, being truncate posteriorly. Its mesial, 
inturned process is somewhat elongate and well developed, with 
the usual pneumatic foramina near its apex superiorly. These 
processes are directed upward and inward, the apex in either 
case being blunt. Each presents two surfaces ventrally, and 
these are smooth. One surface is continuous with that of the 
jaw, the other pertaining to the underside of the inturned 
process. 
Superiorly either one of these articular ends is concaved cen- 
trally, and that surface does not come in contact with the quadrate 
of the same side in articulation. Upon either side of this con- 
cavity, however, internally and externally situated, there is to 
be noted a conspicuous,, articular facet for articulation with 
the corresponding ones on the quadrate of the same side. 
In many publications, here and abroad, I have described the 
skeletons of various species of eagles, falcons, hawks, and their 
