264 IMPORTANT ANATOMICAL LANDMARKS. 



first rib, which it crosses. The interval between the above- 

 named muscles may be obliterated by their great degree of 

 development. 



The not unfrequent extension of the pleural cavity above 

 the clavicle, sometimes to an extent of two and even three 

 inches, will be made apparent on inflating the apex of the 

 lung by a full and forced inspiration, and by percussion. 



CHEST. 



The arteria innominata corresponds in position to a line 

 drawn from the centre of the union of the first with the 

 second bone of the sternum, to the right sterno-clavicular 

 articulation ; by extending the neck its pulsations may be 

 felt. 



The nipple, in the male, lies upon the space between the 

 fourth and fifth ribs. 



The coracoid process of the scapula may be felt below 

 the clavicle, in the interspace between the deltoid and pec- 

 toralis major muscles. The line of this interspace corre- 

 sponds to that of the course of the axillary artery. 



The position of the heart may be determined by percus- 

 sion. " The apex pulsates between the fifth and sixth ribs, 

 two inches below the nipple and one inch to its sternal side. 

 The aortic valves lie behind the third intercostal space to 

 the left of the sternum. The pulmonary valves lie behind 

 the junction of the third rib, on the left side, with the 

 sternum. The tricuspid valves lie behind the middle of 

 the sternum, about the level of the fourth costal cartilage. 

 The mitral valves lie behind the third intercostal space, 

 about one inch to the left of the sternum." 



The bifurcation of the trachea corresponds in position 

 to the line of union between the first and second bones of 

 the sternum. 



The lower margin of the lung, anteriorly, corresponds to 

 the most depending portion of the sixth rib ; laterally, to 

 the eighth rib ; posteriorly, to the tenth rib. It is obvious, 

 therefore, that the pleural cavity may be penetrated with- 

 out the lung being wounded. 



BACK. 



The scapula covers the ribs from the seventh to the 

 tenth, inclusive. 



The bifurcation of the trachea corresponds in position 

 to the spine of the third dorsal vertebra. 



