MONTAGU'S HARRIER. 



145 



species. In the Eagles of the genera Aquila and Halueetus 

 these foramina usually disappear entirely, each side of the 

 breast-bone consisting of an uninterrupted convex plate, 

 and the posterior portion is somewhat tapering instead of 

 being broader than the middle. In the Osprey {Pandion) 

 the hinder margin is still further altered in outline, and it is 

 possible that this peculiarity may be in some way connected 

 with the bird's habit, as described, of taking its prey under 

 water : for, as will subsequently be mentioned, species whose 

 nature it is to seek their food by diving, and are thereby 

 subjected to a greater or less amount of pressure in pro- 

 portion to the depth of water, not unfrequently undergo a 

 considerable modification of this part of the sternum as com- 

 pared with those nearest to them in general structure, but 

 not so expert in their subaquatic feats. 



By an extended examination of the different species of 

 Buzzards and Harriers, it will be found that the characters 

 described as necessary to produce rapid flight decline gra- 

 dually. The sternum decreases in size, the keel loses part 

 of its depth and the coracoid bones and furcula become more 

 slight. 



A representation of the sternum of a Vulture has already 

 been given and that of an Owl will be immediately inserted, 

 to afford a comparative view of the size and structure of the 

 same parts in these Families of the Birds-of-Prey. 



