154 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



quantity of sea-water, simultaneously takes in a large 

 number of the smaller marine animals ; raising its 

 tongue it drives out the water, but retains behind the 

 filter the food that came in with it (Fig. 70). 



In all vertebrates, with the exception of some 

 fishes and a few amphibians (e.g. Pipa), there is 

 developed in the floor of the mouth a tongue, which 

 owes its primitive origin to the mucous membrane 

 which covers the branchial arches. It is never of 



Fig. 69. Last Molars of (A) African, (B) Indian Elephant. 



large size in fishes, and in them is never supplied with 



muscular tissue as it is in the higher forms ; in some 

 . . 



cases it is provided with a horny sheath. 



In many forms, as in some Amphibians (e.g. the 

 frog), where it is attached by its anterior end to the 

 symphysis of the lower jaw ; in Chamseleons, where it 

 is knobbed at its extremity ; and in various other 

 lizards, where it is cleft anteriorly, as it is also in 

 Ophidia, it is capable of considerable protrusion, and 

 may be used as a prehensile organ. 



Among Birds the tongue is protruded with 

 great rapidity by the wood -pecker (Picidse), and 

 by the humming-birds (Trochilidse), and sun-birds 



