16 FOSSIL REPTILIA OF THE 



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

 more concave across than in birds. Between b and c ', e, g, 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, a ). At the 

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

 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. 

 3, 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 Ptero- 

 dactyle as in Tab. Ill, fig. 3, we look almost directly upon the edge of the 

 radial crest (b, j), 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 (b) to be seen. The degree to which the radial crest 

 projected in the humerus of the large Cretaceous Pterodactyle (Tab. Ill, 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 



