450 BRITISH FOSSIL REPTILES. 



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

 vexities 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 CohnnbidcB, 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 (PI. 13, 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 (e), answering to the ulnar crest or tuberosity 

 in the bird. The radial crest (fig. 9, 6) 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 Croco- 

 dilian than the Avian type. The ulnar crest, or tuberosity (c), is rather more 

 prominent and better defined than in the crocodile, but the radial crest (6) 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, ending below by a rough tuberosity, h, projecting at a right angle from 

 the shaft of the bone; the lower sharp margin (fig. 1, i) 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 



