PROTRACTILE MOUTHS 



in the upper part, and marked by definite bony ex- 

 crescences. I see the closed mouth, like a long oblique 

 slit turning downwards; when thus shut, the lower 

 jaw comes against the upper like a trap. 



I press with my finger somewhere about the middle 

 of the lower jaw, thus opening the animal's mouth. 

 Then there is a sudden change. As the lever is 

 pressed, accompanying it exactly, the upper jaw and 

 the surrounding parts move forward and stretch out 

 above the down-bent lower jaw. When this has 

 moved as far as possible; when it leaves the hori- 

 zontal and begins to turn down, it has above it the 

 covering made of the parts so projected, and the 

 whole forms a long, broad tube which, prolonging the 

 great head, amplifies the snout strangely and gives it 

 an entirely new appearance. It is like a mask which 

 has just been put on. Think of an ancient castle 

 whose drawbridge, as it is lowered, takes with it the 

 ceiling and walls of the gateway it protects, so that 

 before anyone can get into the castle he has to pass 

 through a tunnel. Then you have an idea of the 

 general effect of the change produced. If I reverse 

 the operation; if, that is, I lift the lower jaw by pushing 

 it upwards, everything goes back as it was; the parts 

 projected fold up again, and finally the mouth, again 

 becoming an oblique slit, shows no signs of its extra- 

 ordinary powers, which are denoted by the word 

 " protractile," a very suitable word to describe the 

 phenomenon we have just observed. 



This mouth, unlike any to which we are accustomed, 

 has two movements; it opens from top to bottom like 

 any other mouth, but, further, it lengthens and stretches 

 forward. Both movements work together, thanks to 

 a construction which is different from the usual, and 

 to explain this we must make a short incursion into 

 the realm of osteology. 



The two jaws of fishes, like those of other vertebrates, 

 contain as a means of support two skeletal pieces called 

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