THE CHEST. 103 



angle; the shaft is flattened from above downward, and 

 presents on its upper surface two shallow grooves, the 

 inner for the subclavian vein and the outer for the sub- 

 clavian artery. Between these grooves, at the inner 

 border, is the tubercle for the insertion of the scalenus 

 anticus muscle. The under surface has no groove for 

 the intercostal vessels. It is not twisted on its axis, 

 and rests on a plane which both extremities and the 

 shaft touch. The second rib has a slight angle, is but 

 little twisted on its axis, and presents an ill-defined 

 groove along its inferior border posteriorly. 



The tenth rib has a single articular surface on the 

 head, and the angle is not so strongly marked. The 

 eleventh and twelfth ribs have no tuberosity a single 

 articular surface; the eleventh a slightly-marked angle, 

 and the twelfth none at all. The eleventh and twelfth 

 ribs have no attachments to the sternum. 



THE CHEST. 



The chest is an osseo-cartilaginous cage, which in 

 general form may be said to be a truncated cone, flat- 

 tened antero-posteriorly. It_i_s formed behind by the 

 twelve dorsal vertebrae and the ribs to their angles; lat- 

 erally, by the shafts of the ribs; anteriorly, by the shafts 

 of the ribs, costal cartilages, and sternum. Its transverse 

 diameter exceeds the antero-posterior at every plane. 

 Its antero-posterior diameter increases decidedly in pass- 

 ing from the upper to the lower part of the chest. This 

 is due to the increasing length of the fourth, fifth, sixth, 

 seventh, and eighth ribs and costal cartilages thrusting 

 the sternum forward as it descends, and to the strong 

 anterior concave curve of the bodies of the dorsal ver- 

 tebrae. The upper opening of the chest is an osseous 

 ring formed by the first dorsal vertebra, the first ribs and 



