142 SKELETON OF THE DUCK TRIBE. 



the fore part of tlie sternum; it thus forms the chief 

 support of the wing, and the main point of resistance 

 during its downward stroke. In the hawks and other 

 birds of prey, and in the crows and most passerine birds, 

 a small bone (os humero-capsulare) extends between the 

 scapula and coracoid along the upper part of the glenoid 

 cavity; this is absent in the swan and other swimmers, 

 as well as in the gallinaceous and wading birds. The 

 humerus, 53, is usually a long and slender bone, but is 

 not always developed in length in proportion to the pow- 

 ers of flight; for, although it is shortest in the struthious 

 birds and penguins, it is also very short, but much thicker 

 and stronger in the swift and humming birds. The head 

 of the humerus is transversely oblong and convex; it is 

 further enlarged by two lateral crests ; of these the supe- 

 rior is the longest, and is bent outwards; the inferior is 

 thickened and incurved, and beneath it is situated the 

 orifice by which the air penetrates the cavity of the bone. 

 The articular surface at the opposite or "distal" end is 

 divided into two parts, one internal, for the ulna, of a 

 hemispheric form, the other also convex, but more elong- 

 ated and oblique, extending some way upon the anterior 

 surface of the humerus. The extremity of a long bone of 

 a limb which is next the trunk is called the "proximal" 

 one; the extremity furthest from the trunk, the "distal" 

 one; they are not always "upper" and "lower." The 

 ulna, 55, glides upon the inner hemispheric tubercle, upon 

 the trochlear canal, and on the back part of the outer con- 

 vexity. A ligament, extending from the outer part of 

 the head of the radius to the outer part of the olecranon, 

 above the posterior margin of the outer division of the 

 articular surface of the ulna, pla3^s upon the back part of 

 the radial convexity of the humerus and completes the 



