174 Mr Houston on the Structure and Mechanism 



digiously in the throat, so that had the style, which pressed for- 

 cibly ag^nst the integuments under the chin, been elevated, I 

 have little doubt the organ would have undergone a partial 

 elongation. 



The effect on the animal of frequently protruding its tongue, 

 might also be advanced in support of the same theory. An in- 

 terval of rest was always taken between the acts, which I have 

 never seen repeated above six or eight times in succession ; and 

 even this was evidently followed by fatigue. Mere muscular 

 action would not so soon produce exhaustion ; the tongue of the 

 woodpecker, which is protruded solely by this cause, can be shot 

 out many times in quick succession, without the animal's evin- 

 cing any subsequent fatigue. 



When 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 fold- 

 ed 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 far- 

 ther. 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 prehensile 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 the tongue being attained, 

 the mouth opens wider, partly to give more ready admission to 

 the prey, and partly, perhaps, for the purpose of relaxing the 

 muscles, and favouring the return of the accumulated blood ; 



