Chap, iv.] TONGUE OF VERTEBRATES. 157 



opening of the entire tubes, air would, when there 

 is not, rush in instead, and that the advantage of the 

 frayed margins lies in the fact that the honey will 

 ascend to the tubular portion by capillary attraction. 

 It is important to note that these arrangements are of 

 a homoplastic character, inasmuch as the humming- 

 birds are not close zoological allies of the sun-birds ; 

 in other words, we have here again an example of 

 how similar structures are gained by forms which live 

 under similar external conditions. 



In the Parrots the end of the fleshy tongue is 

 diluted, and, from its prehensile function, has been 

 compared to a human finger ; on its lower surface 

 there is a broad nail-like horny plate, which is free at- 

 its anterior border ; in the brush-tongued parrots 

 there are spinous papillae on the upper surface, which 

 stand upright, or project forwards when the tongue is 

 protruded. 



The tongue of Mammals is well provided with 

 muscular tissue, so that it is not only protrusible (it 

 is of great length in insectivorous forms like the 

 ant-eater), but is capable of a licking movement ; 

 and in some, such as the lion, it is armed with strong 

 horny papillae that are of considerable assistance in 

 removing flesh from bones. In man, in addition to 

 the kind of functions just enumerated, it is of impor- 

 tance as an accessory organ of articulate language. In 

 some mammals a tongue-like structure (the subliiigna) 

 is developed beneath the tongue ; in the lemurine 

 Galago (Fig. 71), the front end of this organ is provided 

 with five stiff denticles, arranged in comb-like fashion, 

 and having, apparently, the function of keeping clean 

 the incisor teeth (Flower). In the dog, and some other 

 Carnivora, the protrusible tongue is supported by 

 a fibrous and muscular body, the so-called " lytta," 

 or worm of the dog's tongue. 



The walls of the cavity of the mouth are provided 



