156 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



bones, or bones that support the tongue, are of con- 

 siderable length, form a curve with its concavity 

 forwards, and then, trending forwards, lie on the 

 upper surface of the skull, and reach as far as the 

 nasal region. Attached to these bones, and attached 

 also to the anterior end of either mandible, is an 

 extensor muscle, which lies on the inner or concave 

 side of the loop ; on its contraction the loop is drawn 

 up, and as the only mobile point of the hyoid bones is 

 that at which their anterior extremities are inserted 

 into the tongue, it is clear that the upward movement 

 of the bones must result in the forward movement of 

 the tongue ; in some other Picidse the hyoid bones 

 are movable in their sheath, but the result is the same. 

 Essentially similar arrangements are to be seen in the 

 humming-birds and sun-birds. The mechanical prin- 

 ciple, that the longer the hyoid bones the greater the 

 force and extent of the protrusion of the tongue, is 

 supported by what has been observed in Picus as 

 compared with Zosterops (Gadow). 



The tongue, thus protruded, is in the woodpecker 

 invested in a horny sheath, which ends in a slender 

 point, and is provided on either side with backwardly 

 directed prickles, which serve to draw from the holes 

 in the wood the insects on which this bird feeds ; 

 their capture is aided by the slimy secretion of the 

 salivary glands, which are compressed on the con- 

 traction of the extensor muscle. (Compare the account 

 of the Great Ant-eater, page 160.) 



In the sun-birds the horny part of the tongue 

 forms two tubes ; in the honey-eaters there may be as 

 many as eight, and the inner or outer margins 

 become frayed out into fine processes ; in the 

 humming-birds there are tubes, the edges of which 

 are ordinarily entire. It has been pointed out by 

 Gadow, that while the sucking in of honey is an easy 

 process when there is sufficient fluid to fill the anterior 



