Fig. 57. Wings of a Wild Duck with the coverts removed (Anas boschas). × 1/3.

A. Right wing seen from the dorsal side. B. Left wing disarticulated

and seen from the ventral side. (Brit. Mus.)

1. humerus.10. second phalanx of second
2. radius.digit
3. ulna.11. remicle.
4. radial carpal.12. pennae humerales.
5. ulnar carpal.13. cubitals or secondaries.
6. first phalanx of first digit.14. metacarpal quills.
7. second metacarpal.15. ad-digital.
8. third metacarpal.16. mid-digitals.
9. first phalanx of second digit.17. pre-digital.

(b) The tectrices or coverts are short feathers, which cover over the quills of the rectrices and remiges, and clothe the body generally. Their barbules are less developed than is the case with the quill feathers, so that the barbs separate readily from one another, especially at the base of the vane. The nomenclature of the various patches of coverts on the wings is seen in fig. 56. A small patch of backwardly-directed feathers surrounding the external auditory opening are known as the auriculars.

2. The filoplumes are rudimentary feathers, consisting of a minute stem and slightly developed vane. They are left in the skin after the other feathers have been removed.

3. The plumulae, or down feathers, have the stem very slightly developed, while the barbs are soft and free from one another. They are distributed all over the body, not only among the contour feathers, but also over the spaces (apteria) which bear no contour feathers.

In the young bird the rudiments of the new feathers are formed at the bases of the embryonic down feathers, and as they grow they push them out from the skin. The embryonic down feathers however remain attached to the apices of the new feathers till these have reached a length of about an inch; they are then shed.

II. ENDOSKELETON.