OSTEOLOGY OF BIRDS 



71 



commodate the sacral enlargement of the cord. This gradually con- 

 tracts again at a point opposite the anterior borders of the acetabu- 

 lae. 



The 22d zertebra throws up both parapophyses and transverse 

 processes against the ilia. In this the next three succeeding verte- 

 brae follow suit. This takes place at the narrowest part of the 

 pelvis, and these processes are very stout here. 



In the 26th to the 2pth, inclusive, the short abutting processes can 

 not be seen upon direct ventral aspect. This is the region of the 

 true " sacrum " and the foramina of exit for 

 the sacral nerves are here double on either 

 side, one opening being above another. 



The 30th, 31st and 32d vertebrae have 

 long parapophyses, which amalgamate at 

 their outer extremities, where they form a 

 powerful abutment for the pelvic walls at 

 points opposite the acetabulae. The pelvis 

 of this harrier is deep in all this region, that 

 is, posterior to the 25th vertebra and in- 

 cluding the three I have just mentioned. 



The pelvic bones behind grasp but two 

 more segments of the column, the 33d and 

 34th vertebrae. These much resemble the 

 anterior coccygeal ones, especially the last 

 one. 



In the coccyx we find six vertebrae freely 

 movable on eacli other, but with nothing 

 peculiar about them. The fourth and fifth 

 of this series have equal and at the same 

 time the most far extending transverse processes. The width of 

 the last (the sixth) is about equal to the first, and the last three 

 have bifid hypapophyses. Circus has a very broad and lofty 

 pygostyle, that in the adult bird shows but few traces of its original 

 composition. Its anterior edge is sharp, while ibehind it is flattened 

 and narrowly triangular with the base of the triangle below. I give 

 a posterior view of this bone in the osteology of the Cathartidae 

 above, figure 13, where it is compared with the bone as it occurs in 

 other Fakonidae. 



In Circus pneumaticity is partially extended to the first two free 

 coccygeal vertebrae, but not beyond them. 



In the pectoral arch we find that a scapida is broad and truncate 

 posteriorly, with its apex drawn out into a spicularform point. Its 



Fig. 28 Superior aspect of 

 pelvis of Circus; same spec- 

 imen as the last. Life size 

 from nature 



