(d) Other feathers.—Compare the covert and contour feathers with the quill feathers. Observe, in the contour feathers, the less perfect interlocking of the barbs of those parts which are covered by other feathers.
Pluck the pigeon, and notice the hair-like structures left in the skin. They are called filoplumes. Pull one out and examine it with a lens; it bears a few barbs at its upper end, but these do not interlock.
Examine a nestling-pigeon, and notice the down-feathers which clothe it temporarily. Each is at first covered at the base with a horny sheath. The barbs do not interlock. The down-feathers are pushed off by the growth of the permanent feathers.
5. The plucked pigeon.—Observe that feathers do not grow on all parts of the body, but are confined to definite feather-tracts, which can be recognised by the scars left by the quills. Notice especially the sockets of the large wing-and tail-quills. Make out the oil-gland, a small knob just above the tip of the true tail. It furnishes a lubricating fluid used in preening the feathers. Examine more closely the different regions of the body—the neck, the joints of the limbs, etc., which were disguised by the feathers. The filoplumes have already been seen. Feel the great muscles of the breast, and the edge of the sternum or breast-bone in the middle line. Just in front of this feel the soft crop, with the grain which is probably present in it.
Before boiling the bird in order to separate and examine the bones, open the crop and inspect its contents. Cut away the enormous muscles of the breast (why are they so large?) and open the body-cavity behind and remove the internal organs, being careful not to break any bones.
6. The skeleton.—Boil the bird until the flesh can be easily removed. A small nail-brush will be found useful in cleaning the bones. Keep as many of these in contact as possible, and make out and examine the following parts:
(a) The skull, with the rounded brain-case, horny beak, and large eye-sockets. Notice, at the back of the skull, the single knob, which fits into a hollow on the first vertebra.
(b) The backbone.—Notice the long neck, the fusion of many of the vertebrae in the trunk-region, and, at the end of the tail, the “ploughshare bone.” This last supports the tail-quills.
(c) The breast-bone, or sternum, produced ventrally into a thin plate called the keel (to which were attached the great muscles of the breast), and connected by ribs to the backbone.
(d) The position of the shoulder joint, and the socket for the bone of the upper-arm. Notice the V-shaped “merrythought.”