34 Philippine Journal of Science wis 



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 maxillojugal 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 



