112 NEW YORK STATE MUSEUM 



cheriway, a large, oval pneumatic foramen is always seen ; 

 this may also exist in Polyborus lutosus. 



Few morphological differences of any importance distinguish the 

 skeleton of the pectoral or the pelvic limb of Polyborus 

 lutosus from the corresponding parts in an average Falco. 

 But such as they are, they are very good. They appear only to be 

 referable to the skeleton of the lower extremity, and here we find in 

 the caracara that the femur is relatively shorter and stouter, with a 

 very extensive excavation for the ligamentum teres, and strongly de- 

 veloped processes at its condylar end. The cnemial processes of 

 the tibiotarsus are more prominent, but beyond this the bones of the 

 leg are similar in form to those of Falco mexicanus. 



Coming to the tarsometatarsus we find it to be relatively con- 

 siderably longer than it is in the average Falco, but its chief differ- 



Fig. 55 Right lateral aspect of the sternum of P ol y b o r u s 

 cheri w a y. Natural size 



ence is seen in the hypotarsus. Here the small outside apophysis 

 is much concaved .beneath, while the far larger internal portion, 

 although long, is still distinct and is not produced down the shaft 

 as it is in Falco. A sharp and raised linelike ridge is obliquely 

 thrown out from the laterointernal margin of the summit of the 

 bone, to pass directly down the shaft from a short distance (below the 

 major process of the hypotarsus, forming in doing so the internal 

 boundary to the longitudinal shallow groove, at the posterior aspect 

 of the shaft for the tendons. A similiar line occurs on the opposite 

 side of the shaft. This latter is very straight, the major share of 

 its continuity being of nearly uniform caliber throughout, thus dif- 

 fering much in this respect from the bone in a Buteo. The tubercle 

 for the insertion of the tendon of the tibialis anticus muscle is on 

 the same side of the shaft as it is in the true falcons. 



