EXTERNAL ANATOMY. SCANSORIAL FEET. 13S 
ordinary perchers, but the tarsus is very shorty that is, 
not longer than the hinder toe : the lateral toes are 
either equal or not, hut the middle one is much shorter 
than in the jays and other hird.s, which are both ar- 
boreal and terrestrial. Another peculiarity of the pre- 
hensile foot is seen in the claws, which are short, broad, 
and unusually curved ; by this we know that they are 
well adapted for enabling the bird to take a firm hold 
of branches, while they are totally unfitted for terres- 
trial habits. The common oriole {Oriolus galbu/a) 
will serve to explain this 
® structure in the absence of 
any other native bird; but it 
; is much more perfectly deve- 
loped in the family of short- 
legged thrushes, including 
^ the genera Cliloropsin {fig. 
f ( 69 . a), Bmchypus, Tricho- 
^ phorus, &c., all of which are 
natives of Africa and India. 
The foot of the Ampelis garrulun {h) unites this and the 
insessorial structure, the middle toe being much more 
lengthened than in any of the last mentioned genera. 
(121.) The last form leads us to those of the Sean- 
norial structure, as developed in such birds as have three 
anterior toes, and one posterior. Of such feet as are 
especially adapted for climbing, where the toes are dis- 
posed in pairs, we have already spoken, hut there are 
a great variety of birds possessing the same faculty 
and yet exercising it hy means of feet very differently 
constructed. We shall now trace, in the gradual deve- 
lopment of this structure, aU its variations among birds 
whose toes have the ordinary direction so characteristic 
in the typical perchers. The sort of foot last defined, 
and which we have called prehitnsile, may be con- 
sidered the first incipient development of the scansorial 
structure ; the primary distinctions of which is in an 
unusual elongation of the hinder toe, and a great 
breadth and curvature of the claws. The short-legged 
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