To those who have not given attention to the structure of a bird's wing the following rough description may be of interest. The wing of a bird may be regarded as having two portions: (1) that part to the outer side of the wrist joint. The main feathers of this portion are usually about ten in number, and are known as the primary feathers. (2) That part of the inner side of the wrist joint which may be called the body of the wing. The main feathers of this portion vary according to the length of wing.

(a) A salient characteristic of a bird's wing as a whole is the comparatively rigid and heavy anterior edge and the light yielding elastic posterior margin.