1086 THE THORAX. 



Surgical Anatomy. Paracentesis of the pericardium is sometimes required in cases of effu- 

 sion into its cavity. The operation is best performed in the fifth intercostal space, one inch to 

 the left of the sternum. The operation has been performed, however, in the fourth, sixth, and 

 seventh spaces, and also on the right side of the sternum. 



THE HEART. 



The Heart is a hollow muscular organ, of a conical form, placed between the 

 lungs and enclosed in the cavity of the pericardium. 



Position. The heart is placed obliquely in the chest : the broad attached end, 

 or base, is directed upward, backward, and to the right, and corresponds to the 



FIG. 694. Front view of the thorax. The ribs and sternum are represented in relation to the lungs, heart, 

 and other internal organs. 1. Pulmonary orifice. 2. Aortic orifice. 3. Left auriculo-ventricular orifice. 4. Right 

 auriculo-ventricular orifice. 



interval between the fifth and ninth dorsal vertebrae that is, it lies opposite the 

 sixth, seventh, and eighth vertebrae ; the apex is directed downward, forward, 

 and to the left, and corresponds to the space between the cartilage of the fifth 

 and sixth ribs, three-quarters of an inch to the inner side and an inch and a 

 half below the left nipple. The heart is placed behind the lower two-thirds of 

 the sternum, and projects farther into the left than into the right cavity of the 

 chest, extending from the median line about three inches in the former direction, 

 and only one and a half in the latter. The anterior surface of the heart is round 

 and convex, directed upward and forward, and formed chiefly by the right ven- 

 tricle and part of the left. Its posterior surface is flattened and rests upon the 

 Diaphragm, and is formed chiefly by the left ventricle. The right border is long, 

 thin, and sharp ; the left border short, but thick and round. 



