OSTEOLOGY" OF BIRDS 85 



There is a great similarity between the trunk skeletons of 

 Ictinia mississippiensis and Circus h u d - 

 s o n i u s ; these are the principal differences : in Ictinia there 

 is but one pair of sacral ribs, and consequently there are but six 

 pairs of costal ribs articulating with the sternum. There are seven 

 in Circus. In Ictinia the upper ends of the os furciila meet the 

 scapulae rather more extensively; the epipleural appendages of the 

 ribs do not, as a rule, fuse with Ihe borders of the ribs; and the 

 xiphoidal end of the sternum may be either once notched or once 

 fenestrated upon either side of the keel. I have, as yet, never met 



Ji^ ' 36 



Jis-^'^ 



JL^ . 38' 



bkuUs of Kites 



Fig. 36 Skull of Ictinia mississippiensis 



Fig. 37 Skull ofElanus leucurus 



Fig. 38 Skull ofElanoidesforficatus 



K\\ the skulls are seen upon superior view, and all are slightly reduced in size. They 

 are outline drawings from photographs, and show very well the marked differences in 

 the skulls of these birds as thus compared. 



with a notched sternum in the case of Circus. The pelves of these 

 two birds differ to some extent in form, but these differences in 

 reality are not very great. Usually there are but five of the anterior 

 sacral vertebrae that throw out their lateral processes against the 

 nether walls of the ilia. In Circus there are six. In both, the last 

 four sacrals throw out their parapophyses as braces against the 

 iliac margins upon either side. These are well up towards the dor- 

 sum in Ictinia — not attracting special attention ; in the harrier, 

 on the other hand, their outer extremities are extensively fused 



