195 



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 evincing 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 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 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 ; the os hyoides is 

 drawn back by the sterno-hyoid, sterno-ceratoid, and omo-hyoid 

 muscles ; the lurgescence of the erectile part subsides ; the pouch 



H n2 



