Chap. x.i THE RIBS. 175 



anterior aud posterior axillary lines. If a lower 

 space be selected there is danger of wounding the 

 diaphragm, especially upon the right side. If the 

 eighth or ninth space is selected the incision is made 

 just external to the line of the angle of the scapula. 

 The trochar should be entered during inspiration, the 

 space being widened thereby, and should be kept as 

 near as possible to the lower border of the space, so as 

 to avoid the intercostal vessels. Tapping of the chest 

 through any space posterior to the angles of the ribs 

 is not practicable, owing to the thick covering of 

 muscles upon the thoracic wall in this place, and the 

 fact that the intercostal artery, having a more hori- 

 zontal course than the corresponding ribs, crosses the 

 middle of this part of the space obliquely. Beyond 

 the angle the intercostal vessels lie in a groove on 

 the inferior border of the rib forming the upper boun- 

 dary of the space. The vein lies immediately above the 

 artery, and the nerve immediately below it. In the 

 upper four or five spaces, however, the nerve is at 

 first higher than the artery. 



Owing to the protection it derives from the ribs 

 and the intercostal muscles, it happens that the inter- 

 costal artery is seldom wounded, and when wounded 

 it will be understood that considerable difficulty is 

 experienced in securing the vessel without doing 

 damage to the pleura and adjacent parts. 



Pus may readily be conducted along the loose 

 tissue between the two layers of intercostal muscles. 

 Thus, in suppuration following upon disease of the 

 vertebrae, or of the posterior parts of the ribs, the pus 

 may be conducted along the intercostal spaces to the 

 sternum, and may thus present at a considerable 

 distance from the real seat of the disease. 



Removal of ribs. In order to obtain a free 

 opening into the pleural cavity a portion of one or 

 even two ribs may be excised. 



