THE SKELETON 27 



the furcula, capable of acting as a spring-like 

 connection between the two shoulder- joints, 

 and thus assisting in the formation of a firm 

 basis of support for the wings. 



The stout and slightly curved humerus has 

 an ovoid head for articulation with the scapula 

 and coracoid. On each side of the proximal 

 end there is a prominent tubercle. Close to 

 the medial tubercle is a large opening com- 

 municating with the cavity inside the bone and 

 serving as an entrance for air from the clavicular 

 air -sac. The distal extremity of the bone 

 presents two convex articular areas and a 

 prominence for muscular attachment. 



Of the two bones of the forearm (Fig. 6) the 

 ulna is the larger and carries a small projection, 

 the olecranon, at its proximal and larger end. 

 The slenderer radius is lateral to the ulna in 

 position, the two bones enclosing a wide 

 interosseous space. The proximal end of the 

 radius can be distinguished by a concave 

 articular surface of rounded outline. 



It may be noted that when the wing is 

 folded in rest the bones of the arm and forearm 

 are almost parallel. 



The carpus of the adult contains two bones 

 only — a radial and an ulnar — which represent 



