i 7 4 APPLIED ANATOMY. 



In scoliosis, or lateral curvature of the spine, the distortion is uneven, being a 

 compression of the thorax from above downward and a twisting around a vertical 

 axis. The deformity is frequently so severe as to cause the lower ribs to rest on the 

 iliac crests. It is in order to detect these diseases in their early stages that a know- 

 ledge of the shape of the normal chest is so essential. 



THE STERNUM. 



The sternum consists of three pieces: the manubrinm at presternum, gladiolus 

 or mesosternum, and xiphoid cartilage or metasternum. It is developed in two 

 lateral halves. Should these fail to unite an opening is left in the bone through which 

 the pulsations of the heart have been seen and felt. The junction of the first and 

 second pieces of the sternum is opposite the second rib. The seventh is the last rib 

 to articulate with the sternum directly. 



The first and second pieces of the sternum are connected by a joint which per- 

 sists to advanced age. The projection caused by this joint is called the angiihis sterni 

 or angle of Liidwig. Fractures pass either through this joint, opposite the second 

 rib, or through the bone just below it. They are produced by both direct and 

 indirect force. Usually the upper fragment is beneath the lower one. It is however 

 more true to state that the lower fragment is displaced anteriorly. Any marked pos- 

 terior displacement of the upper fragment would tend to press on the trachea and in- 

 terfere with breathing; the trachea bifurcates opposite the joint. As the pleurae and 

 lungs of the two sides almost or quite touch behind the second piece of the sternum, 

 they may be wounded and emphysema may occur. The heart also may be wounded . 

 Suppuration has followed these injuries, in which case it will be necessary to trephine 

 the sternum to give exit to the pus. The necessity of avoiding wounding of the 

 pleurae in such a procedure is evident, as it would be followed by collapse of the lung 

 and empyema. 



THE RIBS AND COSTAL CARTILAGES. 



The ribs are frequently fractured, sometimes they become affected with caries, 

 and in operating the chest is frequently opened between them or portions of them 

 are excised. They are both elastic and movable, and difficult to break; hence frac- 

 ture is almost always due to direct violence, and this violence may be so great as 

 sometimes to cause death. Normally there are twelve ribs on each side, but some- 

 times there is an extra cervical or lumbar rib. These are both rare, the latter the 

 more so. 



The seven upper ribs are called true ribs because they articulate with the sternum. 

 The remaining five are called false ribs, the eleventh and twelfth being floating ribs. 

 The eighth, ninth, and tenth ribs each articulate by their cartilages with the rib above. 

 The tenth forms the lower margin of the thorax. The eleventh and twelfth ribs are 

 attached only by their posterior extremities, their anterior portion being imbedded in 

 the soft parts; hence they are called floating ribs. The ribs slope downward and 

 forward. This obliquity increases until the ninth rib, after which it decreases. The 

 first rib in front corresponds to the fourth behind, the second, third, fourth, fifth, 

 sixth, and seventh in front correspond each to the fourth rib lower behind. The first 

 rib is the nearest horizontal in regard to its surface and, being well protected by the 

 clavicle, is rarely broken. The intercostal spaces are broader in front than behind 

 and broader above than below. The third is the largest. 



The groove on the lower surface of the ribs holds the intercostal artery, but only 

 as far back as the angle, from which point it occupies the middle of the space. 



The extent of the intercostal spaces is considerably influenced by position flexion 

 of the body brings the ribs together, extension and bending to the opposite side 

 separates them. This point is of importance in reference to the operations of para- 

 centesis and empyema. 



The first costal cartilage unites directly with the sternum, there being no joint 

 present. The second and sometimes the third cartilage is joined to the sternum by 

 a ligament with a synovial joint above and below it. The other costal cartilages are 



