MONTAGU'S HARRIER. 119 



of the types of the Falcons, in order to show in the 

 form and magnitude of the principal bone, and the other 

 bones attached to it, the power of flight possessed by these 

 birds, of which the breast-bone affords good comparative 

 indication. 



The power of flight is one of the decided characteristics 

 of the organization of the class of Birds ; and the division 

 of the Falconidce includes those birds which appear to 

 possess this power in the highest degree of perfection. 

 The conditions necessary to produce this power in its 

 fullest extent are, large and strong pectoral muscles; 

 great extent of surface, as well as peculiarity of form, in 

 the wing; and feathers of firm texture, strong in the 

 shaft, with the filaments of the plume arranged and con- 

 nected to resist pressure from below. The extent of sur- 

 face, the form and other peculiarities of the wings, have 

 been already noticed, and the anatomical part only re- 

 quires to be briefly described. A certain degree of 

 specific gravity is necessary to rapid flight, and this is 

 imparted by large pectoral muscles; the power of these 

 muscles may be estimated by the depth of the keel, and 

 the breadth of the sides of the breast-bone or sternum, 

 as affording extent of surface for the attachment of those 

 large muscles by the action of which the wings are brought 

 down. 



As an illustration of this form, the figure here inserted 

 as a vignette is a representation about one-fourth less than 

 the natural size of the breast-bone of a young male Pere- 

 grine Falcon, which exhibits the depth of the keel, the 

 breadth of the sides, as well as the strength of the coracoid 

 bones ; and the power of flight peculiar to all the species 

 of Falcons is still further illustrated by the form and sub- 

 stance of the forked bone,* commonly called the merry- 



* Which, when the two sides are united, represents both clavicles. 



