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 back, as entirely to conceal its 

 enormous beak, and nearly assume the appearance of a ball 

 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 back-bone 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 

 back-bone are more or less moveable throughout. In the 

 joints connected with the tail, (called the caudal vertebrce,) 

 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 bone is oval, and placed 

 horizontally. 



Another striking feature in the skeleton of a bird is the 

 breast-bone, or sternum, as it is called, which may be 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 bone, 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 bones, 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 bones be strong or weak. Thus in the Penguin, for 



