169

145

more strongly developed in Circus and Buteo than in Aquila. Both first and second
sacral vertebrae have well-defined articular surfaces for the head of a rib ; and there are
indications of a surface for ligamentous attachment of a third free or movable pleura-
pophysis in the pelvis of Harpagornis. the extremity of the long and slender pubis
(Pl. CV. fig. 1, 64) has been broken off in the fossil ; but doubtless it had similar proport-
tions, when entire, to that element of the pelvis in most existing diurnal Raptorial birds.

Humerus. - This bone appears, as is often the case in fossils, to have lost the terminal
angle of the projecting crest (Pl. CVI. figs. 1 & 2,d) called 'pectoral' or ' delto-pectoral':
it is restored in dotted outline after the type of that in Buteo and Circus (ib. figs. 7, 8).
The slight outward bend of the shaft beyond or below this process, which distinguishes
the great wing-bone in the Buzzards, Falcons, and Harriers from that in the Eagles, is
well shown in the photographs, and is noticed by Dr. Haast in the original bone.

The articular head (ib. ib. a) is transversely broader, in proportion to the fore-and-aft
diameter, in both the extinct Harpagornis and in existing Falcons than in Eagles. The
pneumatic ridge or crest (ib. ib. c.p), extending from the ulnar tuberosity to below the
pneumatic orifice, is relatively shorter in Harpagornis moorei than in Aquila chrysaetos ;
the breadth of the entire proximal end is relatively greater in the Falcons than in the
Eagles. The radial tuberosity (ib. ib. b) is more strongly marked in Harpagornis
moorei. In this huge species the graceful sigmoid bend of the entire humerus is better
marked than in the smaller existing Falconines and than in any Eagle ; it suggests a
greater force in the movements of the wing. The longitudinal line (ib. fig. 2,e) along
the palmar aspect of the shaft of the humerus is better marked in Harpagornis moorei
than in the humerus of any existing Raptorial species, though not so developed as to
be termed a ridge. In this character the Falcons make the nearest approach (as in
Pl. CVI. fig. 8, c) to their great extinct confamiliar. In both the line rises to the
character of a ridge as it descends to terminate in the palmar prominence (g) of the
ulnar epicondyle. The radial epicondylar process (f) is characteristically developed in
both the recent (fig. 8) and extinct ( figs. 1 & 2) Falconines. the condyles themselves
(ib. h, i 1) show the usual well-marked modification of that part of the humerus in birds
of flight. The radial (h) and ulnar (i) convexities are strongly marked in Harpagornis
moorei. The least cirumference of the shaft of the present humerus is 2 inches 2 lines ;
it formed part of the series of the smaller (male?) Harpagornis ( II. assimilis, Von Haast),
and is estimated to have been one inch shorter than the humerus in the female (?H. moorei,
Von Haast), of which the shaft only was found.

The radius (Pl. CVI. fig. 4) is thicker in proportion to its length, and also in pro-
portion to the ulna, in Harpagornis, than in existing Raptores. the ridges and
processes indicative of the power of the muscles of flight are strongly marked, espe-
cially the tubercle near the proximal end for the insertion of the main tendon of the
biceps. The shaft is more bent toward the distal end, as Von Haast has observed,
than in existing birds of prey.