54 



rough, with the indication of a ridge along the middle: below this there is a 

 smooth and moderately deep concavity. The anterior border presents a thick 

 rough convexity, forming an obtuse ridge at the middle of its posterior part. 

 The two anterior lateral margins are thinner and slightly concave ; the clavicular 

 ligaments were doubtless attached to these and to the contiguous concavities. 

 The two posterior lateral margins, a, b, present a narrow, elongated, slightly 

 sinuous articular surface for the first sternal rib, and below this a concavity, 

 forming the contracted posterior part of the manubrium. 



Anterior to these emarginations the bone is pinched in, as it were, below the 

 strong transverse ridge, which is continued across the outer surface of the bone, 

 between the posterior ends of the first costal articulations, giving great strength to 

 that part of the sternum. The posterior boundary of the manubrium forms a 

 subquadrate surface, supporting five articular surfaces ; two on each side for the 

 bifid, thickened, articular ends of the second sternal ribs : and the intermediate 

 part, by which it is joined to the second bone, or the first of the series form- 

 ing the body of the sternum. The anterior part of the outer surface of the 

 manubrium is roughened with small irregular ridges, depressions, and vascular 

 perforations ; the ridges upon the concave part of the manubrium are more re- 

 gular in their arrangement, and indicate the interspaces of the attached strong 

 fasciculi of the great pectoral muscle. 



The bones forming the body of the sternum may be divided into two parts, a 

 broad and flat posterior plate of a quadrate form, and an anterior rhomb or cube 

 projecting from the middle of the plate ; and they each present not fewer than ten 

 articular surfaces, two for the contiguous sternal bones, and the remaining eight 

 for portions of two pairs of sternal ribs. 



The second sternal bone* is short as compared with the first, subconcave on 

 each side, and with its posterior plate traversed on the inner or upper surface by 

 a thick, obtuse longitudinal ridge. The external or anterior process is less ab- 

 ruptly continued from the posterior plate than in the succeeding bones : it is 

 shorter than the supporting plate, to admit of the interposition of the anterior 

 extremities of the second sternal ribs, which meet between it and the manubrium, 

 and likewise of the extremities of the third pair of ribs between it and the third 



* PI. IX. fiR. l.II. 



