44 
Philippine Journal of Science 
1919 
they are highly pneumatic in character, and consequently very 
light in weight for their size. 
The os furculum, or fourchette, has the form of a very wide- 
spreading capital U ; the lower part of the arch is not especially 
strong, while it rapidly increases in size from below upward, 
to terminate in immense, free clavicular extremities. Either 
of these is much compressed from side to side, with its great 
superior end accurately molded, externally, to the mesial head 
of the scapula of the same side. When duly articulated, its 
apex barely comes in contact with the anteromesial angle of the 
head of the scapula of the same side. 
The clavicular limbs of the furculum are greatly compressed 
from side to side, and the edges thus formed are sharp, espe- 
cially the mesial ones. There is but small evidence of a hypo- 
cleidium, and the entire bone is powerfully curved backward 
and upward. Its pneumatic foramina are principally situated 
in the concavities of the upper clavicular extremities, upon their 
moderately shallow outer concavities, on that part of the bone, 
upon either side, which goes to complete the foramina! passage 
among the heads of the three bones of this girdle. 
The os furculum in the skeleton of our subject agrees very 
well with the corresponding bone in the harpy eagle; though in 
the latter species the free clavicular ends are more extensively 
rounded off than they are in the case of the Philippine bird. 
Our white-headed eagle possesses a more delicately fashioned 
furculum, while in such a form as Thallasoaetus pelagicus, of 
Korea, the clavicular free ends are enormously developed; but, 
owing to the high, degree of pneumaticity, the bone, as a whole, 
is extremely light in weight. Doubtless other eagles present 
still other differences, not only in the furculum, but also in the 
remaining bones of the girdle. 
When articulated as in life, the coracoids in Pithecophaga do 
not meet in the median line, being separated by an interval of 
several millimeters. Either bone is very massive in form; but 
is light in weight, owing to the high degree of pneumaticity it 
enjoys. All of its parts are conspicuously developed, the broad 
scapular process being perforated by a foramen piercing it from 
before backward. There may be pneumatic foramina of some 
size on the mesial aspect of the big head of the bone and still 
others on its outer aspect. A sternal extremity is considerably 
expanded, the bone in articulation extending beyond the sternum 
laterally. Here it is much compressed from before backward, 
and thickened at its mesial angle. 
