VERTEBRATE SKELETON 



The fore arm, except in Archceopteryx, is longer than the humerus, 

 its bones are slender, the ulna stronger than the radius and usually 

 showing tubercles on the lower side, caused by the bases of the 

 feathers; it also has an olecranon and there may be a small accessory 

 bone at the lower end of the radius over which the extensor tendon 

 passes. 



The acropodium, relatively longest in fast fliers, is most modified. 

 The carpus has the same intracarpal joint, accompanied by reduction 

 of the carpal elements, there being at most, in the adult, two of 

 these (the homologies of which are uncertain), in recent and fossil 



Fig. 311 . — Wing of Clangida 

 (Shufeldt, '09). c, cuneiforme; 

 h, humerus; m, metacarpals; p, 

 phalanges; r, radius; u, ulna; 

 2-4, digits. 



Fig. 312 . — A , B, Two stages in development of wing 

 of Sterna (Leighton, '94) ; C, developing wing of Cyp- 

 selus (Zehntner, '90). c, carpalia; m, metacarpals; /;, 

 humerus; r, radius; re, radiale; ti, ulna; ue, ulnare; 

 2-5, digits. 



birds. The upper and smaller of these articulates with the radius 

 and most of the metacarpals and rests against the ulna. The other 

 (lacking in Apteryx, Casuarius and Dromceus) hes in the angle between 

 ulna and metacarpals which extend to the ulna. In the young there 

 are at least two carpalia which fuse early with the metacarpals. 

 In the metacarpus two bones are fused at their ends in modern birds 

 (three separate metacarpals in ArchcBopteryx) usually with a gap 

 between them. Another smaller bone projecting from the radial 

 side of the first, is another metacarpal; it varies in length and bears 

 one or two phalanges. Digit 3 is the longest and usually has two 

 phalanges, the ulnar digit is much Uke radial. 



There has been much discussion of the numbering of the avian digits — i, 2,3; 

 2, 3, 4; and 3, 4, 5. Since several birds have an additional metacarpal in the 



