CRETACEOUS PTERODACTYLES. 451 



tuberosity, but more especially by the direction of the large, radial crest («), is 

 more concave across than in birds. Between b and c, in fig. 1, it is gently convex 

 lengthwise, and is very smooth. 



A longitudinal ridge (fig. 1, '), along the distal half and palmar side of the 

 base of the radial crest, indicates, as in birds, the insertion of the strong and large 

 pectoral muscle. 



The articular head of the bone is reniform, not uniformly convex, as in birds, 

 but slightly concave between the beginnings of the radial and ulnar crests or 

 processes on that moiety of the head next the palmar side (fig. 3, «). At the 

 opposite (anconal) side (fig. 2, «), the head-piece projects slightly beyond or over- 

 hangs the shaft, the upper part of which, on the anconal side, is slightly concave 

 lengthwise, very convex across, more so than in birds, and without trace of 

 the median longitudinal ridge (/, fig. 7). It is equally devoid of the ridge 

 which, in the crocodile (fig. 18, d), runs close to the radial side of the anconal 

 surface. 



The shaft is more cylindrical than in birds. The pneumatic foramen (figs. 

 2, 5, p) is situated a little below the radial end of the head of the bone, on the 

 palmar side of the bone; in the vulture, and most birds of flight, it is situated on 

 the opposite side (fig. 7, p). The pneumatic texture of the shaft is as well marked 

 as in any bird of flight. 



In looking directly upon the palmar side of the humerus in the bird one has an 

 oblique, foreshortened view of the radial crest, the base of which lies wholly along 

 the radial margin. Taking the same view of the humerus of the Pterodactyle as 

 in PI. 13, fig. 3, we look almost directly upon the edge of the radial crest {h, b'), 

 the base of which has inclined below from the radial upon the palmar surface. 

 A corresponding view of the humerus of the crocodile (fig. 11) shows the whole 

 base of the radial crest on the palmar surface, clear of the radial border, and 

 the opposite side of the crest to that in the bird is obliquely brought into 

 view. (In the figure 11 the radial side of the shaft is rather too much turned 

 towards the eye.) 



In the position and shape of the radial crest the Pterodactyle is between the 

 bird and the crocodile; in the transverse extent of the crest it exceeds both. The 

 crest differs in extent and shape in different species of the Pterodactyle. In fig. 1 

 the ulnar side of the shaft is turned so far towards the eye as to permit the whole 

 breadth of the radial crest {h) to be seen. The degree to which the radial crest 

 projected in the humerus of the large Cretacean Pterodactyle (PI. 13, fig. 1) 

 is only shown at its lower part, the upper, thinner portion being broken away. 

 Relatively to the size of the head of the bone, the extent of the base is greater 

 than in the smaller species of Pterodactyle, a corresponding portion of the 

 humerus of which is represented in fig. 5, from the same aspect as fig. 1. The 



