310 MR. W. P. PYCRAFT ON THE [Apr. 15, 



that the dorsum of the trochlea lies almost behind the level of 

 the 2nd and 3rd. The regularity of the curve is thus bioken. 



Usually the outer and inner trochleas are produced backwards 

 into spur-like processes, that of the outer trochlea being dii-ected 

 backwards, whilst the inner slopes obliquely outwards and back- 

 wards away from the shaft. In some few cases, as in Leptodon 

 for example, these spurs are barely perceptible. 



In Sepentarms, the Cathaitae, and the Falconidse the hypotarsus 

 takes the form of a strong median keel. But whereas in th e two 

 former the keel is grooved equally on either side, and terminates 

 above in a more or less quadiungular table; in the latter it is 

 much more deeply grooved externally, and terminates above as a 

 thin vertical plate with a flanged free border. The front of the 

 tarso-metatarsus in Serpentarius and Cathai'tse is deeply grooved. 

 In the former are two distinct raised surfaces for the tibialis 

 anticus, in the latter only one. Immediately above the surface 

 for attachment of the tibialis anticus are two foramina, large in 

 the Cathartae, small in Serpentarius. 



In the Falconidse the anteiior tarso-metatarsal groove is shallow, 

 the foramina are small, and there is but a single raised process 

 for the tibialis anticus, which lies on the inner side of the shaft. 



In the other Accipitres the hypotarsus takes the form of two 

 more or less prominent spurs separated by a wide gi'oove. The 

 inner spur is generally somewhere near the middle line of the shaft, 

 but in Elanus it springs from the inner border of the shaft. 



The shaft of the tarso-metatarsus is very variable in form. In 

 Serpentarius it is long and cylindiical, but with the inner aspect 

 grooved, but in the majority of the Accipitres it is more or 

 less dorso-ventrally flattened and twisted into long and broad 

 ledges and plates ; thus adding exceedingly to its power. 

 These features are most marked in Thrasa'etus, which in section 

 is seen to be almost — a-shaped. The same is true of Aquila, 

 Halia'etus, Parahuteo, Busarellus, Antenor, Uruhitinga, and 

 Helotarsus, for example, but to a lesser extent. In forms such 

 as Gyjiohierax and Gypaetxis the shaft is much less markedly 

 modified, and4ihis accords well with theii' habits. Polyhoroides 

 has a peculiar shaft. This, as we have previously remaiked, is 

 long, much flattened antero-posteriorly, and deeply gTooved be- 

 hind : its outer border is flattened out into a i-elatively bioad 

 plate, so that in section the shaft resembles that of Thrasa'etus 

 without the lateral torsion. 



The phalanges are also charactei-istic. In Serpentarius the 

 ungual phalanges ai-e large but not remai-kably so. Ph. 1, 2 of 

 digit II. are subequal; ph. 2, 3, digit III. are shorter than ph. 1 ; 

 ph. 3 and 4, dig. TV. are much reduced. 



In Oathartee ph. 1 of the hallux is very long ; the phalanges of 

 digits II., III. are also relatively much longer than in Serpen- 

 tarius or the Accipities. The phalanges 2, 3 of dig. lY. are also 

 longer, relatively, than in other Falconiformes. 



In the Falconidfe ph. 1 of dig. II. is considerably shorter than 



