OSTEOLOGY OF BIRDS IO5 



F . mexicanus has a pelvis as compared with that bone in 

 Buteo 1 i n e a t u s , which does not exhibit so much spreading 

 out on the part of the ilia anteriorly, nor do these bones approach 

 each other so closely over .the " sacral crista/' The " gluteal ridges " 

 are not so sharp nor as prominent, and the postacetabular portion 

 of the bone is not bent downward and forward as much as it is in 

 the Buteo. In the Falco there may be no interruption of the ossifica- 

 tion of the postpubic style, and upon the ventral aspect we observe 

 that there is but one vertebra that has its parapophyses very specially 

 modified as acetabular braces, although the one next behind it is, 

 though to a much less degree. 



Very good characters are to be found in the sternum of Falco 

 mexicanus and other true falcons. We find that the carina 

 extends the entire length of the sternal body, and that its angle an- 

 teriorly is not ever markedly rounded off. Its anterior margin is 

 straighter than in Buteo, and its lower border is not so convex. 

 The manubrium is fairly well developed and somewhat elongated, 

 while above it, in the middle line, on the anterior border of the 

 sternum, there is another process developed, which projects to the 

 front, and serves to retain the coracoids in their sternal grooves. 

 These last mentioned bones very decidedly decussate, lapping each 

 other for fully their mesial thirds, the left one usually (invariably ?) 

 crossing above the right. Posteriorly the xiphosternum always 

 presents a rather large subelliptical foraminal perforation, one upon 

 either side of the keel, but situated near the posteroexternal angle 

 of the bone, and close to the hinder edge. 



Immature or subadult specimens of any of the genus Falco may 

 have broad notches in place of these foramina, formed by a de- 

 ficiency in the posterior margin opposite them. But I believe, in 

 general, the sternum of any true falcon is either 2-notched or 2- 

 f enestrated posteriorly ; and the bone is always pneumatic. 



All the species of this genus, the true falcons, have a very char- 

 acteristic shoulder girdle. The os furcula is U-shaped, without 

 hypocleidium, and with broad laterally compressed limbs. Either 

 free clavicular end is bluntly rounded and transversely thickened 

 where it rests against the scapula. Externally it presents a shoulder 

 for articulation with the head of the corresponding coracoid. A 

 scapula has rather a narrow and somewhat thickened blade, with its 

 hind third slightly expanded with the distal apex pointed. An- 

 teriorly, the scapular head is inclined to be tuberous, presenting 

 quite an extensive surface to the glenoid cavity, and a rather mas- 



