2 
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 (Cafhiida;), also possess 
spiny tails (cf. vol. i. p. 119), as do also the South American 
Spine-tails {Dendrocolaptidcc), 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 ot 
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, Sphyropiens and 
Xenopicits 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 ( Trochilidee) and Sun-Birds i^Nectariniided) 
Tlie 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 Fkidce 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jected or withdrawn as required, the hyoid cornua are pro- ’ 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 j 
top of the skull. The sub-lingual glands are greatly developed, 1 
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 I 
analogous to those found in the Ant-Eaters and several other < 
Mamm.als, and in the Chameleon among Reptiles. 
