14 FOSSIL REPTILIA OF THE 



concave, with the plane of the terminal expansions vertical, as the bone extends 

 along the side of the trunk from its scapulo-coracoid ai - ticulation backward, in its 

 position of rest. 



The head of the humerus is an elongate, semi-oval convexity (Tab. Ill, fig. 8 «), 

 with the long axis transverse from the radial to the ulnar sides (vertical, as naturally 

 articulated), and with the ends continued into the upper (5) and lower ( c ) crests. 

 Of these, the upper one (b, figs. 6 — 8), in the natural position of the bone, is on 

 the same side as the radius, the lower, more tuberous one ( c ), is on the same side 

 as the ulna ; the one marks the " radial" side, the other the "ulnar" side, of the 

 bone. The side of the humerus next the trunk answers to that called " anconal" 

 (fig. 7), the opposite side to that called "palmar" (fig. 6). 



The expanded, proximal part of the shaft on the palmar side (fig. 6) is concave 

 across, convex lengthwise ; on the anconal side (fig. 7) it is convex across to 

 where the ulnar ridge ( c ) bends anconad near the pneumatic orifice (p). 



The radial crest (b) answers to the " greater tuberosity " and to the " pectoral" 

 and " deltoidal ridges " in mammals ; the " ulnar" crest (c) to the " lesser tube- 

 rosity," and the ridge for the "latissimus dorsi," in mammals. 



In a few exceptions the shaft of the humerus is almost cylindrical, in still 

 fewer (e. g., Aptenodytes) it is flat. 



In the vulture (V. monackus), the ulnar crest forms a thick tuberosity at its 

 proximal end (fig. 7, c), projecting anconad, and overarching the "pneumatic" 

 foramen (p) ; it descends a short way obliquely palmad, decreasing in breadth, 

 but still thick, convex, and terminating obtusely (fig. 6, c'). The radial crest 

 (fig. 6, b) better merits the name ; it extends twice the length of the ulnar one, 

 down the shaft, to the palmar side, towards which the whole crest is slightly bent ; 

 its margin describes a very open or low, obtuse, angle at its middle part. A 

 ridge (?•) upon the palmar side of its distal half indicates the boundary of the 

 insertion of the pectoralis major into the crest. At the middle of the anconal 

 surface of the proximal part of the shaft there is a low, longitudinal 

 ridge (ly 



At the distal part of the humerus a ridge on the radial side of the palmar 

 surface, and a rising of the bone on the ulnar side of the same surface, diverge 

 to the opposite angles or tuberosities of the expanded end of the bone ; they 

 include a shallow, sub-triangular concavity above the articular surfaces. These 

 are two, and are convex. 



The radial surface is a narrow, sub-elongate convexity, extending from near 

 the middle of the palmar surface obliquely to the lower part of the radial 

 tuberosity, where the convexity subsides ; it is very prominent at its palmar end, 

 with a groove on each side, the deeper one dividing it from the ulnar, articular 

 convexity. This is of a transversely oval or elliptical shape, most prominent 



