An essay on the structure and mechanism of the tongue of the chameleon / [John Houston].

  • Houston, John, 1802-1845.
Date:
1828
Catalogue details

Licence: Public Domain Mark

Credit: An essay on the structure and mechanism of the tongue of the chameleon / [John Houston]. Source: Wellcome Collection.

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    soon produce exhaustion: the tongue of the woodpecker, whicli is protruded solely by this cause, can be shot out many times in quick succession without the animal’s evincing any subsequent fatigue. ■SVlien the mouth is shut and the tongue at rest, both its erectile and prehensile portions are drawn on the style, the point of which rests against the symphysis of the chin, close behind the front teeth. In this state the prehensile part surrounds the two anterior thirds of the style, and the erectile portion is folded in plaits on its posterior third (Fig. 7. E and H). When the tongue is about to be darted forth, the mouth opens just enough to give it passage, and the style, carrying with it both portions of the tongue, is protruded from the mouth for about half an inch, by the actions of the genio-hyoid, and three cerato-maxillary muscles. The progress of the os hyoides under the skin is visible, and so far it can advance the tongue, but no farther. The prehensile portion, unchanged in bulk, now flies off the style in the direction given it by that bone, and propelled by the erectile portion, which from being so small and pliable as to lie folded on the root of the style, acquires a length equal to the entire body of the animal, a thickness nearly as great as that of the pre- hensile portion, and a rigidity which enables it to advance in a straight line, carrying the latter before it. The stretching of the mucous membrane on the sides everts the edges of the pouch on its extremity, which is thereby expanded to cover the prey with more certainty. The object of the propulsion of tlie tongue being attained, the moutli opens wider, partly to give more ready admission to the prey, and ])artly, perhaps, for the purpose of relaxing the muscles and favouring the return of the accumulated blood ; the os liyoides is drawn back by the sterno-hyoid, sterno-ceratoid, and omo-hyoid muscles; the turgescence of the erectile part subsides; the pouch