394 C. J. Sundevall on the Wings of Birds. 



and the former the strongest. The carpus has only two very 

 small, free hones {v and w) ; the others appear to have 

 either entirely disappeared or become coalesced with the 

 following part (at x). The large os metacarpi {c) belonging 

 to the only finger developed has at its base a large tubercle 

 {sc), which seems to indicate coalescence with a part of the 

 carpus and the metacarpus of the thumb. In some birds 

 this tubercle is produced into a spine (spur) covered with 

 horn ; and it always bears on the anterior (radial) side the 

 small thumb {d), composed only of a single joint. Along the 

 posterior (ulnar) side of the bone lies an os metacarpi (be- 

 tween y and v) of a third finger; but this is amalgamated 

 with the former at the two ends^ and only bears at its apex 

 a small phalange (/) concealed under the skin. The middle 

 finger consists of two joints [y and z). 



At the base [h) the humerus is more or less enclosed be- 

 tween the muscles, so that, although it does not project 

 entirely, as in man, beyond the curvature of the surface 

 of the trunk, it always does so partially (f-^). The cubitus 

 and the hand, which bear the true wing-feathers, are strongly 

 compressed and flattened in consequence of the form of the 

 bones, as well as of the position of the muscles and structure 

 of the skin. 



In the angle behind the humerus the muscles and skin, as 

 in man, form two more or less distinct folds, which bound 

 the axilla (fig. 2, i) ; the anterior fold is formed by the pec- 

 toral muscles, the posterior one by the back and the margin 

 of the scapular muscles. 



In the anterior angle, between the humerus and cubitus 

 the skin does not lie, as usual, closely upon the muscles and 

 bones, but it forms there a large fold (e), the antebrachial 

 fold (plica antebrachialis) . When the wing is folded up, 

 this cutaneous fold would hang loosely down like a bag, if it 

 were not drawn together by a very remarkably constructed 

 elastic sinew, which issues from a muscle in the shoulder 

 (in front of h, fig. 6) beside the m. deltoideus, and runs 

 within the whole anterior margin of the fold as far as the 

 carpus, where it spreads out and terminates in the skin. 



