72 ANATOMY OF VERTEBRATES. 



humeral tubercle for the radius, the fore-arm moves in a plane 

 not quite perpendicular to the palmar surface of the humerus. 

 When the fore-arm is flexed and the wing is folded, the distal 

 end of the antibrachium is near or in advance of the proximal end 

 of the humerus ; the radius being sui:)erior and the ulna a little 

 external as well as inferior. 



The radius is always the more slender bone of the two, some- 

 times in a remarkable degree: its proximal end is expanded, 

 subelliptic, ^^dth a concavity for the oblique tubercle, and a 

 thickened convex border next the ulna for articulation with that 

 bone : a little beyond that articular expansion is the tubercle for 

 the insertion of the biceps. The shaft here becomes slender, 

 usually subcompressed, with a slight bend, convex upward from 

 the ulna ; the rest of the shaft, which becomes subtriedral, showing 

 an opposite flexure toward the ulna, though very slightly marked. 

 The distal end is rather more, though less equally, expanded, 

 from the radial to the ulnar side : rather flattened with one or two 

 tendinal grooves on the anconal side, with a terminal transverse 

 convexity for the scaphoid, produced palmad to articulate "v^dth the 

 ulna ; with a tuberosity (^Aquila) or ridge ( Tachypetes) on the 

 radial side of the expansion. The orifice of the medullary artery 

 in the non-pneumatic radius is on the ulnar side of the shaft about 

 one-fourth from the proximal end. 



The ulna is straio:ht or with a sino-le and slight curve, more 

 marked in the shorter antibrachium of Gallince than in the long 

 one of long-^^dnged waders and smmmers. The proximal end is 

 most expanded, and is obliquely truncate for the articular exca- 

 vation adapted to the ulnar tubercle of the humerus : the obtuse 

 angular production of the ulna, behind or anconad of the cavity, 

 represents in different degrees in different birds the olecranon, 

 but is always short : an extension of the bone radiad is obliquely 

 excavated for the head of the radius. The shaft of the ulna 

 gradually decreases to near the distal end, where the subtriedral 

 is exchanged for the subcylindric shape. A ridge is developed 

 below the head on the ulnar side in Raptores. In birds ( Tachy- 

 petes ^ e.g.) in which the ulna is pneumatic, the foramen is on the 

 palmar surface a little below the head. On the ulnar and anconal 

 sides of the shaft are the two rows of quill-knobs (in Raptores) 

 for the ' secondaries ; ' the anconal row is most marked in longi- 

 pennate Natatores ; and is the only row in many birds. But 

 this character of the bird's ulna is wanting in the flightless and 

 some other birds. The distal end of the ulna slightly expands 

 into a trochlear joint very convex from the radial to the 



