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IGUANAS.
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panded broadly during excitement. It does not, however, form a bag, nor is it susceptible of inflation, as commonly represented, but is simply extended by means of the branches of the tongue-bone (os hyoïdes), which in repose pass down longitudinally beneath the skin. Under the influence of excitement, the tips of this bony fork are drawn downward and forward, stretching the skin with them, in an elliptical form, the two inner surfaces of the skin being in contact.[1] This
- ↑ The apparatus by which this extension is effected was thus described as long ago as 1825, by Professor Bell. “The framework of this structure consists of a remarkable developement of the os hyoides or bone of the tongue. This bone is situated immediately under the larynx. It has two long, slender, bony processes on each side, which, for the sake of distinction, I shall term the anterior and posterior lateral processes,—a small one which is filiform, given off from the anterior part of the bone, and closely connected with the under part of the tongue,—and a very long, delicate, and elastic cartilage, extending from the body of the bone, nearly to the middle of the abdomen, immediately beneath the skin, to the internal surface of which it is attached by condensed cellular tissue. In its form it is slightly flattened and tapering to its extremity, where it is extremely slight and flexible.
“The anterior lateral process extends backwards to the angle of the lower jaw, over the muscles of which it is curved upwards. The posterior lateral process is placed in a similar direction, but does not take the same curve over the edge of the jaw. These two processes run parallel to each other through almost their whole length, but at a small distance apart.
“There are several pairs of muscles attached to these little bones, by the action of which the phænomena are produced, which it is my object to explain. Of these the following are the principal. A broad strong muscle arises from the whole edge of the posterior lateral process, and is inserted into the clavicle. It is consequently of considerable length; and by its contraction the whole bony frame- work is drawn back and a little downwards, so that the distance between the two extremities of the long elastic cartilage being diminished, this organ is thrown into a curve, and the skin of the throat and belly is stretched upon it, exactly as the silk is strained upon the whale-bone ribs of an opened umbrella. The parts are restored to their natural state by the action of [counteracting] muscles.” (Zool. Journ. ii. 12.)
