Montagu's harrier. 105 



it may be desirable, before quitting this group, to exhibit a 

 representation of the breast-bone, or sternum, of one of the 

 types of the Falcons, in order to show in the form and mag- 

 nitude of the principal bone, and the others 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 FalconidiB includes those birds which appear to pos- 

 sess this power in the highest degree of perfection. The 

 conditions necessary to produce this power in its fullest ex- 

 tent 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 connected to resist pressure from 

 below. The extent of surface, the form and other pecu- 

 liarities of the wings, have been already noticed, and the 

 anatomical part only requires 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 Peregrine 

 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 substance of the forked 

 bone,* commonly called the merrythought, which is circular, 

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



