It will be perceived that, in those birds, there is a 

 considerable deviation from the usual means of sup- 

 porting the shoulder. The coracoids are strong, 

 they are well set as far as direction is concerned ; 

 but the smallness of the bases by which they are 

 articulated gives them little stability in the vertical 

 plane. They are, however, strongly tied to the 

 shoulders by means of the large blade bones ; and 

 thus the support of the wing, or rather of the swim- 

 ming flap, is thrown as much upon the muscles of 

 the back, and through these as an elastic medium 

 upon the spine, as upon the sternum. 



As these birds use their imperfectly produced 

 wings only in swimming, or in the leaping motion, in 

 which there is no second effort of the wings in the 

 air, and indeed little or no effort of them there at all, 

 the body is never borne up by those appendages, and 

 thus the organisation of greatest ease to the bird is 

 that in which the upper and the under sides contri- 

 bute equally to its support. In its ordinary habit of 

 being in the water, indeed, it is pressed pretty equally 

 by that fluid upon all sides ; and therefore the great- 

 est stability of the clavicle, which is the bone which 

 resists the compressing force in the motion forward, 

 is more stable by having its hold on the back by 

 means of the large scapular. The clavicle is flat- 

 tened, and placed with the edge forward, so that it 

 presents to the water through which the bird moves 

 the greatest stiffness which could be obtained from 

 the same portion of bone ; and its articulation at 

 the shoulder is such that, when there is a strain on 

 the middle part of it, it tends to pull the scapular for- 

 wards. This the broad scapular resists, and it is aided 

 in its resistance by the anterior lateral processes of 

 the sternum, while the equal supports, which the flap 



