104 NATURAL HISTORY OF KERGUELEN ISLAND. 



occupied by the articulations of sternal ribs, about junction of anterior 

 and middle thirds. Here the ridge is re-enforced by the thickened line, 

 limiting externally the area of origin of pectoralis medius. At the pos- 

 terior edge of costal process it bifurcates, becoming continuous on the 

 one side with the ridge limiting coraco-sterual articulation, and with the 

 external and posterior margin of the costal process on the other. The 

 area occupied by the origin of pectoralis medius is the thinnest part of 

 the bone. Keel begins strictly at apex of mannbrial process, whence a 

 sort of beak is given off, its margin looking downward and backward 

 for 0.30 inch. Then follows a sharp angle, with a quite deeply exca- 

 vated curve, backward, down"ward, and forward again, to the most 

 prominent part of the rostrum. The anterior border of the keel is 

 therefore quite deeply concave, and its anterior extremity pointed. Its 

 inferior border is slightly convex, and runs backward and upward, 

 bifurcating at its extremity to join the angles of the expanded gladiolus. 

 It measures along its curve 2.1, and at its deepest part, opposite the 

 anterior angle, 0.80 inch. Its anterior border is much thickened by 

 a stout ridge, proceeding backward and downward from the internal 

 angle of sternocoracoid articulation. 



Coracoid measures 1.30 inches in length, and consists of a subcylin- 

 drical shaft and two expanded extremities, bearing three articulating 

 facets. The scapular extremity is produced upward and forward, ter- 

 minating in a prominent facet for the articulation of the clavicle. This 

 articulating head arches over inward, so as to constitute, by aid of a 

 coracoscapular ligament, a considerable foramen continuous upon the 

 coracoid with a deep groove which runs down upon its lower face, and 

 is bounded by a ridge of bone internally. Three-tenths of an inch above 

 and behind the anterior end of the coracoid is a broad articulating 

 surface, extending entirely across the posterior face of the bone, for the 

 scapula. At the external junction of scapula and coracoid is the glenoid 

 cavity. The shaft of coracoid is interiorly convex, superiorly flat, and 

 toward its posterior end slightly concave. It sends off a remarkable 

 sickle-sliaped spine from the outer side of its posterior head, which curves 

 slightly upward and extends just to the extremity of the costal process 

 of sternum. Internally to this, on its posterior margin, is a triangular 

 spine, extending backward, which fits into a corresponding depression 

 in the ridge limiting sterno-coracoid articulation. From this spine the 

 articulating facet extends inward, arching upward at the same time, 

 and measures 0.40 from without inward. Including the external spine 

 above referred to, the bono measures .03 across its base. 



