THE CONTENTS OF THE THORAX. 



101 



lage. The highest point of the pleural dome, projected upon the anterior surface of the body, 

 is situated 3.0 centimeters above the anterior extremity of the first rib. 



The pleural limits are those situations in which the three chief portions of the parietal pleura 

 become continuous with each other. In addition to the dome of the pleura, containing the apex 

 of the lung, the anterior and the inferior limits of the pleura are of importance in medical exami- 

 nation. The anterior pleural limit is at the deepest portion of the costo-mediastinal sinus and 

 corresponds to the situation in which the costal pleura is reflected posteriorly behind the sternum 

 to become the mediastinal pleura. The inferior pleural limit is at the lowest portion of the costo- 

 phrenic sinus. As the lung almost completely fills the pleural cavity, the pleural limits during 

 inspiration practically coincide with the anterior and inferior pulmonary margins. Inferiorly 

 the pleural cavity extends almost to the origins of the diaphragm. In figures 45 and 46 the 

 pleural limits are indicated by red lines. Upon the right side the pleural limit commences ante- 

 riorly at the middle of the sternoclavicular articulation, runs toward the median line, which it 

 follows downward to the sixth rib, passes outward along the lower border of the sixth rib, crosses 

 the seventh rib in the mammary line, reaches the lower border of the ninth rib in the axillary 

 line and the eleventh rib in the scapular line, and strikes the twelfth rib at the vertebral column. 

 [The relations of the pleura to the twelfth rib are of importance to the surgeon especially in con- 

 nection with operations on the kidney. When this rib is not abnormally short, the pleural 

 reflection crosses it opposite the outer border of the erector spinae muscle, hence an incision may 

 be carried deeply as far as the angle formed by the twelfth rib and the outer border of the erector 

 spinae without entering the pleura. When, however, the twelfth rib does not reach the outer 

 border of the erector spinae, an incision carried upw r ard into the apex of the angle between this 

 muscle and the eleventh rib is almost certain to wound the pleura. Internal to the outer edge of the 

 erector spinae the pleural reflection lies below the level of the twelfth rib and not infrequently 

 descends as far as the transverse process of the first lumbar vertebra. Cunningham's "Text- 

 book of Anatomy."] Upon the left side the pleural limit extends anteriorly almost to the median 

 line, and passes outward at the level of the fourth rib, so that at the seventh costal cartilage it 

 is about five centimeters distant from the anterior median line in the horizontal direction. The 

 left pleural limit then follows about the same course as upon the right side, but extends a trifle 

 lower in the axillary line. The importance of these relations will be referred to in the descrip- 

 tion of the pericardium. The pleural limits vary, to a certain extent, in different individuals. 

 When one lung is diseased, it is frequently observed that the pleural sac containing the healthy 

 lung extends beyond the normal limits as a result of the vicarious employment of this lung (Fig. 50). 



The lowest portion of the costo-phrenic sinus is not completely filled by the lung, even in 

 deep inspiration. As a matter of fact, the diaphragm is in contact with the inner thoracic wall 

 in this, region during quiet respiration. When there is an abnormal collection of fluid in the 

 pleural cavity, the diaphragm may be pressed downward and away from the thoracic wall; if the 

 fluid is removed by tapping (thoracocentesis), however, the diaphragm rises again and comes 

 in contact with the thoracic wall as before. In this manner the puncture may become occluded 

 and hinder the withdrawal of the fluid. It consequently follows that, as a general rule, the opera- 

 tion should not be employed below the sixth intercostal space in the posterior axillary line. In 

 the back the puncture may be made as low down as the ninth intercostal space. The absorp- 



