CRETACEOUS FORMATIONS. 15 



palmad; all the part of the end of the humerus forming the two articular 

 convexities is as if bent toward the palmar aspect. The ulnar end of the ulnar 

 convexity is bent, and continued anconad to that end of the ulnar tuberosity. 

 An oblique, longitudinal channel divides the anconal end of the radial tuberosity 

 from an almost longitudinal ridge, which is nearer the middle of the anconal side 

 of the distal end of the humerus ; a similar, but shorter, longitudinal ridge or 

 rising of bone, terminates in the anconal part of the ulnar tuberosity. Between 

 the above almost parallel ridges the anconal surface is nearly flat transversely; 

 it is traversed along the middle by a low, narrow, longitudinal ridge. Lengthwise 

 the bone is here convex. 



The differences in the humerus of different birds are seen chiefly in the forms 

 and proportions of the proximal crests ; the radial one in the Columbidce, e. g., is 

 shorter and more produced than in most birds of flight. The humerus in the 

 swift and humming-bird is distinguished by special modifications. 



In the crocodile (Tab. Ill, figs. 9 — 12), the articular head of the humerus 

 (fig. 12, a) is a transversely elongated, sub-oval convexity ; it is continued upon 

 the short, obtuse, angular prominence ( c ), answering to the ulnar crest or tuberosity 

 in the bird. The radial crest (fig. 9, S) begins to project from the shaft at some 

 distance from the head of the bone ; it is shorter, thicker, more prominent, 

 and projects more directly palmad than in the bird. The humerus presents a 

 similar sigmoid flexure lengthwise to that in the bird, but the ulnar contour 

 of the shaft, as it descends from the ulnar end of the head of the bone, describes 

 a concave line to the ulnar condyle ; the radial contour is sigmoid, and not 

 affected by the radial crest, as in the bird. There is a longitudinal ridge 

 (fig. 10, d) on the anconal surface close to the radial border. 



The humerus of the Pterodactyle (ib., figs. 1 — 5) is shorter in proportion to 

 the expanse of its proximal end than in either the bird or crocodile, and it 

 appears to have a straighter shaft. It conforms at its proximal end more with 

 the Crocodilian than the Avian type. The ulnar crest, or tuberosity (e), is rather 

 more prominent and better defined than in the crocodile, but the radial crest (5) is 

 much more developed than in either the crocodile or bird. It resembles that 

 of the crocodile in being more directly bent palmad, or what would be outward in 

 relation to the side of the trunk, in the natural position of the bone at rest. 



The crest begins, above, at the radial and palmar end or angle of the articular 

 head of the bone, and rapidly expands, bending palmad, with a base co- extensive 

 with one fifth of the length of the humerus, inclining, as it descends (fig. 3), to the 

 palmar side, and ending below by a rough tuberosity projecting at a right angle from 

 the shaft of the bone; the lower sharp margin (fig. 1, V) of the tuberosity passes by 

 a quick curve, and subsides upon the cylindrical shaft. The palmar surface of the 

 proximal part of the humerus, by the production in that direction of the ulnar 



