144 FALCONID^J. 



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 connected to resist 

 pressure from below. The extent of surface, the form and 

 other peculiarities of the wings, have been already noticed, 

 and the anatomical part only requires to be briefly described. 

 A certain degree of weight is necessary to 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 moved. 



As an illustration of this form, the figure, inserted as a 

 vignette, on the opposite page, 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 or furcula, commonly called the merry- 

 thought or wish-bone, which is circular, broad and strong, 

 affording a permanent support to the shoulders. This furcula 

 represents the clavicles of mammals. 



Though the subject of the figure may be taken to shew 

 the general form of the sternal apparatus in the Falconidce, 

 various members of the Family present some differences which 

 it may not be inexpedient to notice briefly. Thus the size of 

 the foramina or holes pierced in the posterior portion of the 

 sides of the breast-bone varies not inconsiderably in certain 



* Those who wish to study the mechanics of flight cannot do better than con- 

 sult Prechtl's * Untersuchungen iiber den Flug der Vogel' (Wien : 1846) and 

 Prof. Marey's 'Memoire surle vol des insectes et des oiseaux' as published in the 

 ' Annales des Sciences Naturelles' (Zoologie, 5th ser. vol. xii.). In English the 

 essays of Dr. Pettigrew (Trans. Linn. Soc. vol. xxvi.) and Captain F. W. Hutton 

 (Phil. Mag. August, 1869) may also be mentioned in connection with the same 

 subject; but some of the conclusions of both the writers last named have been 

 i mpugned. 



