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: [Pg 269] (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.” (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.