OSTEOLOGY OF BIRDS II3 



In- the skeleton of pes, Polyborus practically agrees with the 

 typical representatives of the genus Falco. 



So much for the present of the osteology of Polyborus. 



That wonderfully interesting forms of falconine birds occur in 

 other parts of the world, that show in their skeletons a must curious 

 combination of buteonine, falconine, and polyborine characters, there 

 can be no doubt. 



For instance in the skull of Herpetotheres cachin- 

 nans [U. S. Nat. Mus. Collec. nos. 18445, 18446] we see the 

 general form of that part of the skeleton as it occurs in a true Falco, 

 but the upper mandible is unnotched upon either side of its apex; 

 the arrangement of the maxillo palatines and vomer on the basal 

 aspect is as in Buteo, but viewing the first named elements laterally, 

 we find them large, bulbous and smooth, and filling the rhinal 

 chambers as in Polyborus. This bird also has rudimentary basi- 

 pterygoid processes, and the supraorbital parts of the lacrymals are 

 large. A good sized ramal vacuity occurs in the mandible. Its 

 sternum is neither notched nor fenestrated. The articulation of the 

 bones of the shoulder girdle is as in Falco, and I find upon one 

 side the scapular process reaches round to the head of the coracoid 

 with which it articulates. 



Micrastur brachypterus offers a most interesting study 

 in its skeleton, and I am only sorry that, the skull of the specimen 

 before me is very imperfect [U. S. Nat. Mus. Collec. no. 13493]. 

 The superior osseous mandible reminds us very much indeed of 

 Polyiborus, including the great spongy portions of the maxillapala- 

 tines. Upon basal aspect, however, these latter, including - the vomer, 

 resemble the arrangement in Buteo, or in other words they are in 

 extensive contact with the prepalatines, while in Falco these maxillo- 

 palatines stand clear of these parts. 



'Micrastur has a point of great interest in its shoulder girdle, for 

 here at last we meet with a form wherein the broad scapular process 

 of the coracoid curves upward and outward and extensively fuses 

 with the anterior surface of the head of the bone, thus completely 

 closing in the tendinal canal. Upon these parts the clavicle 

 is molded, making also extensive articulation with the scapula. 



The shaft of the humerus in Miscrastur is much curved, but one 

 of its most remarkable bones is the pelvis. Here the ilia for their 

 preacetabular parts face almost directly outward, and are exten- 

 sively in close contact in the middle line. Viewed ventrally, it will 

 be seen that the pelvic basin is transversely much contracted, the 



