SKELETON OF THE WILD DUCK. THE WING. 323 



upwards, while the dorsal surface of the antibrachium looks 

 partially outwards and upwards, and that of the manus mainly 

 outwards. 



The brachium or upper arm contains only a single bone, 

 the humerus (fig. 57, 1). This is a large nearly straight bone 

 expanded at both ends. The proximal end is specially ex- 

 panded, forming two tuberosities, and a large convex head 

 articulating with the glenoid cavity. The pre-axial tube- 

 rosity is the smaller of the two, but is continued by a 

 prominent deltoid ridge, which extends for a very short 

 distance down the shaft. The postaxial tuberosity is the 

 larger, and below it there is a very deep pit, the pneumatic 

 foramen, which leads into an air cavity in the shaft of the 

 bone. The shaft is long and straight, and at the distal end 

 of the bone is the trochlea with two convex surfaces, one 

 pre-axial with which the radius articulates, the other post- 

 axial for the ulna. 



The fore-arm or antibrachium consists of two bones, 

 the radius and ulna. These are of nearly equal length, and 

 are separated from one another by a considerable space except 

 at their terminations. 



The radius (fig. 57, 2), the pre-axial and smaller bone, is 

 straight and fairly stout ; its proximal end articulates with 

 the humerus by a slightly cupped surface, while its distal end, 

 which articulates with the carpus, is convex and somewhat 

 expanded. 



The ulna (fig. 57, 3) is longer, stouter, and slightly curved. 

 Its proximal end is expanded, forming two surfaces which 

 articulate with the trochlea of the humerus ; behind them it 

 is drawn out into a short blunt olecranon process. Its 

 distal end is less expanded, and articulates with the carpus 

 and also with the radius. 



The Manus. This includes the carpus or wrist, and the 

 hand. 



The Carpus. While in the embryo the carpus consists 



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