308 MR. W. p. PYCRAFT ON THE [^P^'' l^J 



and is slightly bowed forwards. The cnemial crests are not 

 largely developed. 



In Serpentarius they form prominent outstanding blades, not 

 extending down the shaft but stiictly confined to its proximal 

 extremity. The ectocnemial crest is directed outwards, standing 

 at right angles to the entocnemial. In so far as the direction of 

 this crest is concei'ned, it agrees with the remaining Falconi- 

 formes, but in its greater size it stands alone. Furthermore, the 

 shaft of the tibio-tarsus is peculiai', in that it is perfectly straight 

 and almost cylindiical, not bowed forwards and depressed as in the 

 other Falconiformes. The tibio-tarsus thvis much more closely 

 resembles that of the Storks. Additional Stork-like charactei'S 

 ai-e found at the distal end of the shaft in the great breadth of 

 the extensor bridge, and in that the lateral borders of the 

 posterior trochlear surface are produced backwards and upwards 

 into a pair of pi'ominent ridges. But there is no intercondylar 

 tubercle, and no depi'ession below the extensor bridge. The 

 ti'ochlese are not laterally compi-essed, but separated by a wide and 

 deep gorge. There is a conspicuous entocondylar tubercle. The 

 fibular crest is but feebly developed, but the fibula extends down 

 to the lower third of the shaft. 



The tibio-tarsus of the Cathartse is much more Accipitrine in 

 character. The fibular crest is prominent. The extensor bridge 

 is wide, oblique, placed nearer the inner border of the shaft, and 

 somewhat more superficial than in the other Falconiformes. 



In the Falconidse and Buteonid?e there is not much difference, 

 save in minor points, some of which, however, are extremely 

 helpful for diagnostic purposes. 



Take the Falconidse for example. In Herpetotheres, immediately 

 above the outer tibial condyle, and laterad of the extensor bridge, 

 is a shallow pit. This, in Polyhorus, becomes pierced by a 

 small foramen opening inwards into the extensor groove. In 

 the remaining Falcons {Herpetotheres being the exception) and 

 in Milvago this small foramen has increased to an aperture as 

 lai-ge as that below the extensor biidge. Thus there appears to 

 be two extensor bridges, one above each condyle. Apart from 

 size, the tibio-tai-sus of Herpetoiheres can easily be distinguished 

 from that of Polyborus by the fact that in the latter the bridge is 

 wider and the intercondylar gorge is narrower and deeper.. 



In the Buteonidfe the most aberrant tibio-tarsus is that of 

 Paixdion. One of its most striking chai-acters is the extreme 

 depth and width of the extensor groove, which is so deep that it 

 is saved from perfoiuting the shaft only by a very delicate plate 

 of bone. The fibula extends to within a short distance of the 

 tarsal segment, and is veiy large. The fibular ridge is placed 

 somewhat lower down the shaft than usual. The distal end of 

 the shaft, above the extensor bridge, is wider than across the 

 condyles, which are lateially compressed. 



It is a point of considerable interest to notice that the extensor 

 gi'oove in the Striges is barely pei'ceptible in the Bai-n-Owl.s,^ 



