34 
Philippine Journal of Science 
1919 
the accessor pieces on the lacrymals. Upon summing up its 
cranial characters, however, it is very evident that it is not as 
nearly related to Pithecophaga as is the golden eagle (No. 18802, 
United States National Museum) (Plate II, fig. 2). 
All eagles thus far examined by me possess, upon lateral 
aspect of the cranium, a deep, rounded, separated crotaphyte 
fossa; a large, squarish postfrontal process; and a squamosal 
projection. This does not show very well in fig. 1 of the present 
memoir, due to faulty lighting of the skull; nor do we, in the 
same figure, gain any idea of the enormous capacity and depth 
of the orbit that exists in the cranium of our subject. Indeed, 
it measures as much as 3 centimeters from the lower edge of the 
postfrontal process to the edge of the subcircular vacuity in the 
interorbital septum in Pithecophaga. This vacuity is also to be 
seen in the cranium of the golden eagle, but not in the white- 
headed species of North America. The anterior wall of the 
brain case in our subject is markedly concaved on its anterior 
aspect, and nonperforated beyond the usual foramina for vessels 
and nerves, all of which latter are comparatively small and 
individualized. So far as I have examined their crania, this is 
more or less true of all eagles. 
As will be observed in Plate I, fig. 1, the quadratojugal bar 
in this monkey-eating eagle is quite straight, and of nearly 
uniform caliber from one end to the other. It is so in all true 
aquiline species, and in some the maxillo jugal suture persists 
throughout the life of the individual. 
A quadrate is a big, stout bone, with a well-developed orbital 
process, and a broad, smooth surface on its outer aspect. A 
broad, longitudinal valley lies between the two thoroughly se- 
parated articular facets that occur on its lower mandibular por- 
tion. It presents two heads for articulation with the skull, and 
they are separated by a wide, smooth notch. Nearly all parts 
of this cranium are pneumatic, and to this the quadrate forms 
no exception. 
Either pterygoid bone is small, straight, short, and slender. 
When duly articulated, it does not come in contact with its fellow 
of the opposite side. In the golden eagle the outer margin of a 
pterygoid is very sharp and thin. This aspect in the white- 
headed eagle is longitudinally grooved, and the posterior extrem- 
ity of the bone possesses an upturned process for additional 
articulation with the quadrate. 
All true eagles possess a vomer, which is a long, thin plate 
