28 



THE VOYAGE OF H.M.S. CHALLENGER. 



powerful ligament wliicli binds the base of the coracoid bone to the inner or thoracic 

 surface of the sternum. Surmounting this tubercle is a sharp bony spine which projects 

 forwards, and afl'ords attachment in the recent state to a strong fibrous band, between 

 which and the inner margin of the shaft of the bone the artery of supply to the middle 

 pectoral muscle passes forwards. 



The distal extremity of the coracoid is curved obliquely downwards and inwards, 

 and articulates by its apex with the articular surface developed on the anterior border 

 of the clavicle. Opposite the point of junction of the shaft with the curved extremity 

 of the bone, is the articular surface, which, together with a corresponding one. on the 

 scapula, completes the glenoid fossa for the reception of the head of the humerus. The 

 inner surface of the curved extremity of the bone is deeply grooved, and serves as a 

 pulley over which the tendon of the pectoralis medius plays after escaping from the 

 foramen triosseum. 



The only varieties which I have noticed in the configuration of the coracoid bone 

 occur in the genera Aptenodytes and Pygosceles. In both of these (PL VII. fig. 6) the 

 osseous bar which in the other genera forms the inner boundary of the foramen, through 

 which passes the nerve to the pectoralis medius, is represented only by ligament. 



In Spheniscus the osseous bar in question is relatively more slender than in Eudyptes, 

 and in one species (Spheniscus minor) I found the bar so thin that the circumference of 

 the foramen was deficient at one point. This occurred on the left side only, the right 

 coracoid differing in no respect from that of Eudyptes chrysocome. 



The following table shows the dimensions of the coracoid bone in difi'erent species in 

 inches. 



