THE BONES. 37 



joints of the spine or backbone are more or less movable 

 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 com- 

 pared to the bottom part of a boat resting on a deep project- 

 ing 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 facilitat- 

 ing 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 instance, where 

 the wings are little more than fins assisting in diving, or the 

 Ostrich and Cassowary, where they are so small and insig- 

 nificant as merely to assist in balancing their bodies when 

 they run, the keel of the breast-bone is entirely wanting, or 

 the furcula or merry-thought very imperfectly developed. On 

 the other hand, in the Eagle and Hawk tribe, they are pro- 

 portionably strong, conspicuous, and well defined. 



The bones of the wings next come under observation ; and 

 these, as may be expected, in birds of prey, and some others, 

 which have to carry their food frequently to a considerable 

 distance, or live much in the air, are of great length ; whereas, 



