FEET OF BIRDS. 403 



ated from the model of quadrupeds in giving much greater 

 length to the division corresponding to the foot. At the 

 same time that the foot is brought forwards, the toes are 

 lengthened, and made to spread out so as to enclose a wide 

 base, over which the centre of gravity is situated. The ex- 

 tent of this base is so considerable that a bird can, in general, 

 support itself with ease upon a single foot, without danger of 

 being overset by the unavoidable vacillations of its body. 



The femur is short compared with the tibia, which is ge- 

 nerally large, especially in the order of Grallx^ or wading 

 birds: the fibula is exceedingly slender, and always united, 

 at its lower part, with the tibia; and there is a total deficien- 

 cy of tarsal bones, except in the Ostrich, where rudiments 

 of them may be traced. Already we have seen, in ruminant 

 quadrupeds, that these bones have dwindled to a very small 

 size, but here they have wholly disappeared. The long 

 bone which succeeds to the tibia, though considered by some 

 anatomists as the tarsus, is, properly, the metatarsal bone, and 

 in the Grallcc is of great length. At its lower end it has 

 three articulations, shaped like pulleys, for the attachment of 

 the three toes: there is, besides, in almost all birds, a small 

 rudiment of another metatarsal bone, on which is situated 

 the fourth toe. The number of bones which compose each 

 respective toe appears to be regulated by a uniforjn law. 

 The innermost toe, which may be compared to a thumb, con- 

 sists invariably of two bones: that which is next to it in the 

 order of sequence has always three; that which follows has 

 four; and the outermost toe has five bones: the claws in eve- 

 ry case being affixed to the last joints, which have, therefore, 

 been termed the ungual bones. This remarkable numerical 

 relation, among the several bones of the toes, exists quite in- 

 dependently of their length. 



There is one whole order of ])irds which are particularly 

 fitted for climbing and perching upon trees, having the two 

 middle toes parallel to each other, and the inner and outer 

 toes turned back, so as to be opposed to them in their action. 

 They are thus enabled to grasp objects with the greatest fa- 



