THE BONES. 39 



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 this stiffening or con- 

 solidation 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 fly- 

 ing ; 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 themselves* 

 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, fan-like 

 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 compared to the bottom part of a boat resting on a 

 deep projecting 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 atten- 

 tion 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 i'orked-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 Pen- 

 guin, for instance, where the wings are little more than 

 fins assisting in diving, or the Ostrich and Cassowary, 



