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 structure of a wing than the perfect gradation in strength and stiffness, as well as in modification of form, which marks the series from the first of the primary quills to the last and feeblest of the tertiaries. Now, the sharpness or roundness of a wing at the tip depends on the position which is given to the longest primary quill. If the first, or even the second primary is the longest, and all that follow are considerably shorter, the wing is necessarily a pointed wing, because the tip of a single quill forms the end; but if the third or fourth primary quills are the longest, and the next again are very little shorter, the wing becomes a round-ended wing. The common rook and all the crows are examples of this. The peregrine falcon, the common swallow, and all birds of very powerful flight, have been provided with the sharp-pointed structure."

FIG. III.—STERNUM OF THE PIGEON.

The mechanism by which the wing is moved has now to be described. Tt consists of the mass of muscles on the front of the chest. The sternum, or breast-bone of the pigeon. Figure III., has an exceedingly deep keel, a, serving for

FIG. IV.—MUSCLES OF THE WISH OF THE PIGEON.

the attachment of the powerful muscles which form the great mass of flesh on the breast. These muscles, as shown in Figure IV., pass from the keel of the