| OCR Text |
Show 308 MR. W. P. PYCRAFT ON THE [^Pr- 1^» 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 strictly 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 concerned, it agrees with the remaining Falconiformes, but in its greater size it stands alone. Furthermore, the shaft of the tibio-tarsus is peculiar-, in that it is perfectly straight and almost cylindrical, not bowed forwards and depressed as in the other Falconiformes. The tibio-tarsus thus much more closely resembles that of the Storks. Additional Stork-like characters are 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 prominent ridges. But there is no intercondylar tubercle, and no depression below the extensor bridge. The trochlese are not laterally compressed, 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 Buteonidse 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 later-ad of the extensor bridge, is a shallow pit. This, in Polyborus, 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 large as that below the extensor bridge. Thus there appears to be two extensor bridges, one above each condyle. Apart from size, the tibio-tarsus of Herpetotheres 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 Buteonidse the most aberrant tibio-tarsus is that of Pandion. One of its most striking characters is the extreme depth and width of the extensor groove, which is so deep that it is saved from perforating the shaft only by a very delicate plate of bone. The fibula extends to within a short distance of the tar-sal segment, and is very large. The fibular ridge is placed somewhat lower dowTi the shaft than usual. The distal end of the shaft, above the extensor bridge, is wider than across the condyles, which are laterally compressed. It is a point of considerable interest to notice that the extensor groove in the Striges is barely perceptible in the Barn-Owls, |
