148 COUES ON THE OSTEOLOGY 



its projection forward ; at the same time the outline of the crest of the keel is such that 

 when the inequalities of the bone are all filled up with muscular tissue the resulting sur- 

 face becomes flat, and broad as well as long, affording the best possible outline for contact 

 with the water. 



Coracoids. These are very short, and exceedingly broad and stout. Each measures just 

 three inches in extreme length. The "shaft" proper of the bone is reduced to a minimum 

 of length, nearly the whole bone being taken up by the articular and other processes at 

 the base and head. 



The base of the bone is expanded into a broad, flat, trapezoidal surface, the sides of the 

 trapezoid being all more or less concave. The postero-internal side is concave, smooth, 

 and thin, fitting accurately into the articular groove in the sternum. The antero-internal 

 border is simply a concave outline, running forward to become the inner edge of the shaft 

 of the bone. The antero- and postero-external borders of the trapezoid are the most con- 

 cave of all, being formed by a quite acute process of bone which runs directly outwards 

 exactly under the costal process of the sternum. 



On the inner aspect of the shaft of the bone, just internal to the coraco-scapular articu- 

 lation, there is a lateral expansion of the bone, which curves upwards and forms the pulley 

 over which glides the tendon of the pectoralis minor, in its passage to its insertion into the 

 head of the humerus. This lateral expansion forms by its superior surface a good part of 

 the coraco-scapular articulation. Its inner tip forms a little of the superior coraco-clavicular 

 articulation. 



On the shaft of the bone inferiorly there extends downward towards its head a stout 

 thick ridge terminating in a convex, somewhat oval process, which bears upon its inner 

 face a semilunar facet for the inferior or principal coraco-clavicular articulation. The ex- 

 ternal and superior aspect of the bone has a flat broad dilatation terminating in a convex 

 facet lined with interarticular fibro-cartilage, forming the inferior half of the glenoid cavity. 

 Upon the superior aspect of the shaft, just internal to the preceding facet, there is the 

 somewhat semilunar facet for the coraco-scapular articulation. 



Clavicles. These bones are altogether weaker, and meet at a more acute angle, than 

 we should expect to find in a bird possessed of the powers of flight of the Loon. The 

 ano-le formed by their divergence is scarcely more than 45°. At their broadest part, which 

 is near their origins, they are over half an inch wide, but exceedingly thin. This width 

 decreases rapidly towards the symphysis, where the bones are very weak and slender, and 

 oval or elliptical on a transverse section. The symphysis is a simple fusion of the two 

 clavicles, without any projecting lamella or process, and unconnected except ligamen- 

 tously with the apex of the sternal keel. Each of these bones articulates in two places 

 with the coracoids, as has been already pointed out. From these articulations the bones 

 when in situ dip at first directly downwards, then with a very convex outline run back- 

 wards, at last curving upwards again to the symphysis with a considerable degree of 

 convexity. From the peculiar articulation of these bones with the coracoids at two points 

 it results that the curved surface which serves as a pulley for the play of the tendon of the 

 pectoralis minor is converted into a complete bony canal. 



Besides the proper articulation of these bones with the coracoids, they are throughout 

 their whole extent bound to the latter by a dense layer of fascia, the supraclavicular, 

 which is stretched vertically between the bones. 



Scapula. The scapula, as in most birds, is simply a long, narrow, flattish bone, lying 



