OSSEOUS SYSTEM OF AVES. 69 



into the upper and lower crests. Of these, the upper one, in the 

 natural position of the bone, is on the same side as the radius, the 

 lower more tuberous one 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,' the opposite side to that called ^ palmar.' The 

 expanded, proximal part of the shaft on the palmar side, fig. 6, 

 is concave across, convex lengthwise : on the anconal side it is 

 convex across to where the ulnar ridge bends anconad near the 

 pneumatic orifice. The radial crest answers to the ^greater 

 tuberosity,' and to the '^pectoral' and ^ deltoidal ridges' in mam- 

 mals ; the ^ ulnar ' crest to the ^ lesser tuberosity ' and to the ridge 

 for the ^ latissimus dorsi,' in mammals. In a few exceptions the 

 shaft of the humerus is almost cylindrical ; in still fewer {Apteno- 

 dytes) it is flat ; in the Albatross it becomes triedral toward the 

 distal end. 



In the Vulture ( V. monachus) the ulnar crest forms a thick 

 tuberosity at its proximal end, projecting anconad, and over- 

 arching the ^ pneumatic ' foramen ; it descends a short way ob- 

 liquely palmad, decreasing in breadth, but still thick, convex, and 

 terminating obtusely. The radial crest 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 u23on 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. The 

 tuberosity at the proximal part of the ridge gives insertion to the 

 middle pectoral. 



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 palmad ; all the part of the end of 

 the humerus forming the two articular convexities is as if bent 



