VERTEBRATA. AVES. 



Although this is not the place to enter into details 

 of anatomy, there are yet one or two of the bones 

 which we may slightly notice. The most remarkable 

 bone in the skeleton is the breast-bone, (sternum,) 

 which is very large, spreading, like a shield, over 

 the bowels. From its surface rises a projecting 

 plate, affording, with the sides, a large surface for 

 the attachment of the strong muscles that produce 

 the downward stroke of the wing. The great mus- 

 cular force necessary for this motion, of course, has 

 a tendency to draw the shoulders towards each other, 

 but this is effectually resisted by the expansive 

 power of the united clavicles, called the forked bone, 

 or, more familiarly, the " merry-thought." The 

 greater the power of flight, the more this bone is 

 arched, and the stronger is its resistance. The spine 

 has very little motion, the joints being, as it were, 

 soldered together, and the ribs are nearly fixed ; 

 the skeleton thus resembles a hollow box of bone, 

 with little power of motion in its several parts, 

 except in the limbs. 



