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 



