MUSCULAR SYSTEM. The muscles of birds con form, in general, with the vertebrate type, though the homologies, especially about the fore limbs, are sometimes obscure. For these homol ogies, Newton's review in Brollies Thier-Reicle (Fogel, pp. 9-325) is complete, and is epito mized in the former's Dictionary of Birds, pp. 602-620. Specified arrangenuonts of muscles and tendons, especially the plantar tendons, have been much experimented with as a basis of classi fication, but the results have not proved of great value when taken alone. Only 'a few general considerations need he presented here. The mus cular system of birds is characterized by an extraordinary strength in those parts concerned with activity and endurance, and has certain interesting automatic functions. Thus the vast pectoral muscles attached by a broad fleshy base to the sternum and narrowing to a complicated tendinous attachment to the wing-bones, are mainly two, forming the thick whitish 'breast' of edible fowls; they depress the wing—the effec tive movement. in flight. An elastic band in front of the wing passes from the head of the humerus to the carpal joint; when the wing is extended it is stretched about three times its ordinary length, and its natural contraction enables the bird to keep the wing closed without effort. As
it lies just beneath the skin, it is easily cut, and as such a severance prevents the wing from being firmly extended, it offers the be.st. method of rendering captive birds incapable of flight; to disable one wing is quite enough. See Aluscu LAR SYSTEM, EVOLITTION or.
"In the hind limb of most birds there is a singular extensor muscle, which arises .from the pubis. ends in a tendon which passes to the outer side of the knee-joint, and terminates in the leg by uniting with the flexor digitorum perforatus. The result of this arrangement is, that the toes arc flexed whenever the leg is bent upon the thigh, and, consequently, the roosting bird is held fast upon his perch by the weight of his own body." (Huxley, Anatomy of rcrte bratcd Animals, New York, 1878.)