PROTRACTILE MOUTHS 



of the maxilla and the lower jaw. Consequently, when 

 the latter drops to allow the mouth to open, it forces 

 the upright branch of the premaxilla to come down 

 in a forward swinging movement, and the horizontal 

 branch, also coming forward, slips over the ridge of 

 the palatines. The upper edge of the mouth, thus 



Fig. 22. — Head of a John Dory, mouth open and protruded. 



carried along, cannot but take the maxilla with it. 

 As these parts separate when they move, they diverge 

 like the arms of a compass. Their connecting mem- 

 branes spread out, but still fill the spaces between. 

 The snout thus moves forward and projects, forming 

 a spacious tube, opening outwards at one end, and 

 allowing access to the back of the mouth at the other. 

 When the mouth closes, the lower jaw rises and 

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