110 SURGICAL ANATOMY OF 



serve to break the effect of shocks or blows upon the 

 shoulder or upper limb. On the right side the sterno- 

 clavicular articulation is immediately in front of the in- 

 nominate artery and subclavian vein, whilst on the left 

 it is in relation with the left subclavian vein and the 

 interspace between the left common carotid and subcla- 

 vian arteries ; the interclavicular space lies immediately 

 in front of the trachea. Posteriorly and below, the 

 sternum is covered by the triangularis sterni muscles, 

 and laterally is in relation with the internal mammary 

 vessels. The sternum is liable to fractures, and disloca- 

 tions from it of the clavicle an accident which may 

 occur in any direction but downwards, owing to its close 

 relation with the cartilage of the first rib. 



The costal region, which is bounded anteriorly by the 

 sternum, laterally by the sides of the bodies of the ver- 

 tebrae, and inferiorly by the diaphragm, presents several 

 points of surgical importance, since it contains the mam- 

 mary gland and the intercostal spaces. It is covered in 

 anteriorly and posteriorly above by structures belonging 

 to the region of the upper extremity, in front by the 

 greater and lesser pectoral muscles with their aponeuroses, 

 and behind by the scapula and the muscles attached to 

 it, and between the external borders of the scapular and 

 pectoral muscles, the ribs and the humerus, is a special 

 region, the axilla. 



The intercostal spaces vary considerably in extent: 

 thus they are larger during inspiration; the most re- 

 markable variation in the interspace is at its middle, as 

 during expiration the ribs occasionally approximate so 

 closely that their edges are in absolute contact. The 

 operation of paracentesis thoracis or tapping the thorax, 

 in pleurisy, emphysema, or the pointing of an hepatic 



