OSTEOLOGY OF BIRDS III 



Although there are 19 vertebrae between the skull and the pelvis, 

 as in Falco, they show one interesting difference in that only the 

 four leading dorsals fuse together to form one bone, all the cervicals 

 being free. There are three pairs of cervical ribs, none of which 

 are with epipleural appendages, which is also the case with the pair 

 of sacral or pelvic ribs. These latter have haemapophyses that 

 reach the costal border of the sternum, making six pairs of costal 

 ribs thus articulated. The vertebral ribs are not very stout or 

 broad and their rather small unciform processes fuse with them. 

 In a specimen of Polyborus cheriway [Polyborus 

 t h a r u s , U. S. Nat. Mus. Collec. no. 18478] these processes are 

 most peculiar in that they are much expanded on some of the mid- 

 ribs, which expansion not being very perfectly ossified in some cases, 

 causes the process to he two or even three pronged. There are 

 seven free tail vertebrae, with a very large pygostyle, its bladelike 

 part being very deep anteroposteriorly, and the long superior border 

 convexed. Most important among the characters of the pelvis is to 

 note that there is hardly any bending forward of the postacetabular 

 half of the one at all ; the ilia meet each other only for a short 

 distance over the middle of the broad sacral crista, and the anterior 

 or preacetabular moieties of these bones are peculiar in that they 

 are faced almost directly outward, and look only slightly upward. 

 The postpubic style is entire, being only slightly thinned at the point 

 where it is interrupted in the Buteos. The ends that protrude be- 

 hind are rather heavy. 



There are 13 vertebrae apparently in the pelvic sacrum; the five 

 leading ones throw out their lateral processes against the under 

 surface of the ilium upon either side ; the ninth one has its para- 

 pophyses much lengthened for the support of the bone in the imme- 

 diate rear of the acetabulae. Over either antitrochanter the ilium 

 arches conspicuously, and in the recess it thus forms are seen the 

 pelvic pneumatic foramina. 



Essentially, in its general form, the sternum agrees with the ster- 

 num of Falco, but here in Polyborus it is always 2-notched, a rather 

 large, rounded one occurring on either side of the keel, and the 

 lateral processes thus formed are g-enerally longer than the xipho- 

 sternum. The carinal angle is inclined to curl upwards; the manu- 

 brium is falconine ; and the mesial lip of bone on the anterior ster- 

 nal border, sometimes develops, and may be quite broad. Just 

 within the anterior border of the sternum in Pol y b orns 



