ALLEN'S NATURALIST'S LIBRARY. 



THE WOODPECKERS. SUB-ORDER PICI. 



Externally these birds may be distinguished by their " zygo- 

 dactyle " foot. " Yoke-footed " is another name frequently 

 applied to them, but, described in simple language, they may 

 be said to have two toes "in front " and two " behind." This 

 may seem a very unscientific way of characterising the Wood- 

 peckers, but it is the first character to look for in one of 

 these birds. Then they have usually a stiffened tail of sharp- 

 pointed feathers but not in every case, for the Wrynecks 

 and Piculets have soft-plumaged tails, while some Passerine 

 Birds, such as the Tree-Creepers (Ccrthiida), also possess 

 spiny tails (cf. vol. i. p. 119), as do also the South American 

 Spine-tails (Dendrocolaptid(Z\ so that this cannot be reckoned 

 a peculiar characteristic of Woodpeckers. Then, again, turn- 

 ing to anatomical structure, we find that the Woodpeckers 

 have a long and extensile tongue, the bones of which, the 

 "hyoid cornua" as they are called, extend backwards ovei 

 the skull. The tongue, thus capable of extension, and of 

 enormous length, is furnished with muscles which enable the 

 bird to dart it out and retract it in the most extraordinary 

 manner. This extensile tongue is found in the Wrynecks as 

 well, but is not a character exclusively diagnostic of the Wood- 

 peckers, for two North American genera, Sphyropicus and 

 Xenopicus have an ordinary tongue, as in the majority of Pas- 

 serine Birds. On the other hand, an extensile tongue is found in 

 the Humming-Birds ( Trochilidce] and Sun-Birds (Nectariniidce) 



The following description of the mechanism of the Wood 

 pecker's tongue is copied from that given by Sir William Flowei 

 in the Bird-Gallery of the British Museum. 



" In the majority of the Picida the tongue is long, vermiform, 

 pointed, and barbed at the tip. To permit of its being pro- 

 jected or withdrawn as required, the hyoid cornua are pro 

 longed backward, sliding in a sheath which curves round the 

 top of the skull. The sub-lingual glands are greatly developed, 

 secreting a viscid fluid which covers the tongue and causes in- 

 sects to adhere to it. The peculiar modification of these 

 organs and their application in procuring food are closely 

 analogous to those found in the Ant-Eaters and several other 

 Mammals, and in the Chameleon among Reptiles, 



