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muscles of birds

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muscles of birds - Muscles of birds
muscles of birds - The muscles of a bird are what is popularly known as its flesh. When the skin is removed, the bones are seen to be covered by a mass of this flesh, which is of a red colour, darker in some birds than in others. For instance, in a Duck the colour is a dark red; in a Pigeon, quite a pale brown. The flesh is not, however, merely a thick sheet covering the bones: it can be separated into layers which are themselves made up of a number of separate pieces of muscle. These individual muscles are very commonly of a spindle-like shape, being thickest in the middle and dwindling towards both ends, where they often end in a tough substance called the tendon, which has a glistening and very characteristic appearance. All muscles are not of this form - sometimes they are strap- shaped; and not all of them end in tendons. As the most important act of the bird's life that depends upon its muscles is flying, it is not surprising to find that the muscle which effects the downward stroke of the wing is the largest. This muscle is known as the great pectoral, and it is said to be almost as large as all the other muscles of the body put together. The way in which a muscle effects the movements of the bones to which it is attached is by contracting. All muscles are able to contract; they shorten, and, accordingly, the ends, with whatever they happen to be attached to. are brought closer together. The contraction is governed by the nerves, and it has been discovered that the nerves actually end in communication with the fibres of which the muscle is composed. This pectoral muscle lies on the breast-bone, and nearly completely covers it; indeed, only the edge of the keel appears, and a very little tract at the sides. When this muscle is dissected away another muscle, not nearly so large, comes into view underneath it; this is called the pectoralis secundus. or the second pectoral. Its action is precisely the reverse of that of the great pectoral: it pulls the wing up instead of down. Between them, these two muscles do most of the work in flying. Naturally, in the ostrich tribe, which do not fly, they are much reduced in bulk. But they are never absent altogether, even in the Apteryx, which is, perhaps, further removed from the possibilities of flight than any other bird.

A very curious muscle runs into the patagium of the wing, which is that fold of skin which lies between the shoulder and the hand. This muscle is called the patagial muscle. It starts from the shoulder as a fleshy band, but soon ends in two long tendons: one of these follows the upper margin of the patagium, and finally ends in the wrist; the other passes down over the patagium, and ends below in connection with some of the muscles of the arm, and also by being attached in a fan-shaped way to the skin itself. The function of this muscle is to assist in the folding up of the wing when it is, so to speak, put away after use. The tendons in which the latter part of this muscle ends often show a most complicated branching in the patagium; they frequently offer characteristic differences in different birds, and are made some use of by the systematist. The bird has got a biceps to its arm just as we have. It sometimes happens that this biceps gives off a muscular slip, which runs into the patagium and becomes attached to the upper of the two tendons of the patagial muscle. A good deal of stress is laid by certain ornithologists as to whether this biceps slip is absent or present. Several of the common British birds will afford material to the beginner to ascertain for himself some of the chief variations in these and the other muscles of the body. It will be a good exercise to get a few birds, and to carefully dissect two of them, belonging to as widely different kinds as possible, side by side. You might select, for instance, a Crow and a Pigeon, which are fairly extreme types. To revert to our account of the muscular anatomy of a bird, it will be impossible to attempt any comprehensive account of this branch of the subject, because the facts are so appallingly numerous. We shall content ourselves, therefore, with the mention of a highly characteristic bird muscle which occurs in the leg. This muscle is known as the ambiens. This muscle is thin and ribbon-like. It takes its origin from a little process of the pubic bone usually called the prepubic process. From this point it runs along the inside of the thigh until it reaches the knee; it then bends over the knee and comes out on the other side, where it runs down the leg to join the deep flexor muscle of the foot. When this ambiens muscle contracts it pulls upon the flexor muscle, already referred to; the effect of this is that the toes are brought together by the tendons in which the last-mentioned muscle ends. The ambiens is far from being universally present among birds. It is notably absent from the passerine birds (the Sparrows, Crows, Rooks., and small perching birds generally), and from the Hornbills, Toucans, Woodpeckers, and that varied assemblage known as picarian birds. On the other hand, the Storks, Hawks, and most of the larger birds, have the muscle. But among some of these it is absent; thus, the Owls on the one hand, and the Herons on the other, have no ambiens; but from their general resemblance in other particulars to birds which have an ambiens, it was thought by Professor Garrod that the loss in them was a recent event, and that they might be fairly placed in one great group of birds with an ambiens which he termed, somewhat lengthily, the ' homalogonatae,' or normal-kneed birds, reserving the name ' anomalogonatae,' or abnormal-kneed birds, for the passerines, &c., without an ambiens.

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brain of birds

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lungs and airsacs of birds

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