STERNA OF THE GREBES. 373 



continuous bone as of two posterior lateral processes, 

 which are divided from the central part of the bone 

 by notches of considerable depth. These processes 

 are much stronger, as well as shorter, than those of 

 the birds in the preceding family. They are arched, 

 rising upward at their divisions, and recurving again 

 toward the middle portion, though not joining it. 

 The keel is well developed, though its height is not 

 equal to the breadth of one side of the sternum. It 

 is convex on the under side, and concave in front, with 

 the angle sharp, but without any production of bone. 

 The margin is triangular and cartilaginous. The 

 coracoids are of moderate length, rounded on their 

 anterior sides, and flattened and much enlarged in the 

 rear. They are strong, and well set for giving firmness 

 to the shoulder-joint, as they form a considerable angle 

 with each other, and also with the general line of the 

 sternum ; so that the strain which they exert when 

 the wings are moved is directed toward the point of 

 greatest resistance in that bone, which is, of course, 

 also the mean centre of the surfaces to which the 

 muscles which move the wings are attached. The 

 clavicle is long, forming a regular semi-ellipse, 

 attached by a small tubercle at the middle to the 

 angle of the keel, flattened laterally, and forming, from 

 the head of the coracoid to the keel, a perfect arch, 

 with its convex side to the front, and the terminations 

 of its branches bear against the heads of the scapulars, 

 the greater part of which is slender, and slightly bent 

 downwards. The general shape may be seen in the 

 following two figures of the sternal apparatus of the 

 eared grebe half the size of nature. 



The breadth of this sternum, the convexity of its 

 under side, the form and size of its keel, the strength 

 and setting of the coracoids, and the opening and 



