l6 UNIVERSITY OF MISSOURI STUDIES 



containing the common carotid artery. On the left side 

 the thoracic duct is along with the ascending cervical ves- 

 sels. 



If a needle v\^ere inserted directly backward through 

 the middle of the sternal head of the sternomastoid about 

 2 cm. above the clavicle it would enter the highest part of 

 the apex of the lung. The needle would pass through the 

 skin, platysma and sternomastoid muscles between the in- 

 ternal jugular vein and the thyreoid gland, through the 

 common carotid artery and into the space containing the 

 vertebral and ascending cervical vessels. On the left side 

 it would pierce the thoracic duct. In each case the highest 

 part of the apex lies a little internal to the interspace be- 

 tween the two heads of the sternomastoid. 



The anterior border of the right lung is very indistinct 

 above but is more plainly marked below. From the apex 

 it passes downward behind the upper border of the sternum 

 a little internal to the sternoclavicular articulation, and re- 

 mains behind the right half of the sternum down to the sixth 

 sternochondral articulation, where it becomes continuous 

 with the inferior margin of the lung (Plates XXVIII and 

 XXXII). The anterior border of the left lung is more 

 plainly marked above than that of the right. It is deeply 

 concave below where the heart encroaches upon this lung 

 more than upon the right one (Plates XXVIII and XXXII). 

 Beginning at the apex the anterior border may be traced 

 downward and inward behind the left sternoclavicular and 

 first sternochondral articulations. It passes to the left of 

 the sternum in the first intercostal space and runs downward 

 and outward to the middle of the fourth intercostal space in 

 the midclavicular line. Here it turns inward, crosses the 

 fifth rib 1 cm. internal to the midclavicular line and becomes 



