THE BONES. 
37 
p. 31, affords a still more curious instance of this power of 
movement in the neck, nestling its head so completely 
among the feathers of its hack, as entirely to conceal its 
enormous beak, and nearly assume the appearance of a hall 
of feathers : in which form, secured from all exposure 
to cold, it sleeps through the night. The reason of this 
deviation from the form of skeleton common to other 
animals, is that the stiffening or consolidation in the parts 
of the hack-hone is essential in order to give strength and 
steadiness to the trunk in the violent muscular motion 
required by the act of flying ; for in those birds which do 
not fly, as the Ostrich and Emu, the joints of the spine or 
hack-hone are more or less moveable throughout. In the 
joints connected with the tail, (called the caudal vertebra ,) 
certain other peculiarities in number and form present them- 
selves, adapted to the habits of the bird. In the Martin 
and Swallow, where great freedom in the pliability of the 
tail is necessary, they are most numerous ; whereas in the 
Cassowary, which has no tail, the last joint only is found. 
This last varies also in form in different birds ; for instance, 
in the Peacock, whose beautiful, fanlike spread of tail- 
feathers is so well known, this last hone is oval, and placed 
horizontally. 
Another striking feature in the skeleton of a bird is the 
breast-hone, or sternum, as it is called, which may he com- 
pared to the bottom part of a boat resting on a deep pro- 
jecting keel. From the upper sides of the fore parts of this 
bone two others project, called clavicles, from the extremities 
of which a hone, in the form of the letter V, is projected, 
called the furcula, though better known by the name of the 
merry-thought. Our attention is more particularly directed 
to these three hones, on account of their great importance in 
facilitating the powers of flight ; since it is by the clavicles 
that the wings are connected with the breast-bone, and it is 
by the forked-like furcula, or merry-thought, that the wings 
are kept at a proper distance in flight. Accordingly, we 
shall find, that in proportion to the bird’s necessities, will 
these hones be strong or weak. Thus in the Penguin, for 
