THE THORACIC CONTENTS 509 



In the interval which is left between the two pleural sacs 

 behind the lower part of the left half of the sternum, the 

 pericardium comes into direct contact with the anterior thoracic 

 wall (p. 510). 



The Costo - Diaphragmatic Line of Pleural Reflection 

 indicates the lowest limit of the pleural sac. Although some- 

 times a little lower on the left side, it may, for practical purposes, 

 be mapped out on the surface on the two sides of the body by 

 similar lines. It begins at the lower end of the costo-mediastinal 

 line and passes laterally and downwards behind the seventh 

 costal cartilage and the seventh intercostal space. In the 

 lateral line (mid-clavicular or mammary), the costo-diaphragmatic 

 line crosses the eighth rib, at its junction with its cartilage. It 

 continues to descend slightly as it passes round the body, and 

 in the mid-axillary line it cuts the tenth rib. On the posterior 

 aspect of the trunk the line of reflection ascends slightly as it 

 passes towards the vertebral column, and crosses the eleventh 

 and twelfth ribs, the latter at the point where it is crossed by the 

 lateral border of the sacro-spinalis (see also p. 275). It reaches 

 the vertebral column at the level of the twelfth thoracic spine, 

 i.e. nearly half an inch below the head of the twelfth rib 

 (Fig. 84). 



The Lower Border of the Lung lies at a much higher level 

 than the costo-diaphragmatic line during quiet respiration. 

 In the lateral (mammary) line the lower border of the lung crosses 

 the seventh rib and lies about i inches above the lower limit 

 of the pleura. In the mid-axillary line the difference is most 

 marked and a distance of three or four inches separates the 

 lower border of the lung, which is placed on the eighth rib, from 

 the lower limit of the pleural sac. Posteriorly the difference 

 is not so great, but the phrenico-costal sinus extends usually 

 two inches below the lower border of the lung, which corresponds 

 to the tenth thoracic spine (Fig. 84). On the right side of the 

 body the phrenico-costal sinus is related to the liver and, 

 posteriorly, to the upper pole of the right kidney (p. 275). On 

 the left side it comes into relation successively with the left 

 lobe of the liver, the stomach, the spleen (p. 320), and the upper 

 pole of the left kidney. 



The Anterior Border of the Right Lung is straight and 

 coincides with the costo-diaphragmatic line of pleural reflection. 

 The Anterior Border of the Left Lung possesses a deep notch 

 at its lower end, which falls short of the lateral margin of the 



