(e) The bones of the fore-limb (wing).—Make out the parts belonging to the upper-arm, fore-arm, and wrist and hand, and notice that the bones of the wrist and hand are firmly fused together to give increased strength.
(f) The large hip-bones.—Notice their forward extension and fusion with the joined vertebrae of this region, and the resulting increased firmness of this part.
(g) The bones of the hind-limbs.
7. Pneumatic bones.—Examine the bone of the upper-arm of the pigeon and notice, just below the head of the bone, a small hole which leads into the interior. Break the bone across; is it hollow or solid? Does the inside contain marrow? How does it differ from the corresponding bone of a rabbit?
8. Different breeds.—Examine various breeds of domestic pigeons, and compare them with the common variety, as regards colour, shape, method of flight, extent of feathering of the hind-limbs, etc.
Birds.—It is probable that no class of animals has been more studied than that of the birds; and the reasons for this are not difficult to find. The wonderful power of flight—rivalled only by the insects—and the perfect adaptation of structure to this power; the habits, always interesting and in many cases showing a curious parallelism to human institutions; the beautiful voices of song birds; the grace of movement; the mysteries of migration; and, it may be added, the remarkable story of the origin of birds which has been revealed by modern zoology,—form a combination of characters, at once familiar and elusive, which has greatly stimulated human sympathy and imagination. It is well to begin the study of birds by first taking one familiar species and examining it somewhat closely, and afterwards comparing and contrasting other members of the class. Such a convenient type for study is found in the dovecote pigeon.
Fig. 178.—Pigeons.
The pigeon.—The body of the common dovecote pigeon ([Fig. 178]) is ovoid in shape, tapering gently at the neck and appearing, in the living animal, to pass insensibly into the head. The fore-limbs are modified to form a pair of wings, which are set on a little above and in front of the centre of gravity of the body. Except during flight the weight of the body is entirely supported by the hind-limbs or legs, which are fixed almost exactly below the centre of gravity of the body, i.e. in the best imaginable position. Each foot bears four toes, the first of which is directed backwards. Each toe is armed with a claw.