THE HEART AND PERICARDIUM 203 



The serous layer of the pericardium lines the inner surface 

 of the pericardium, and is continued on to the surface of the 

 heart, being also prolonged over the vessels in the pericar- 

 dium. The aorta and pulmonary artery are enclosed in one 

 sheath, and it surrounds the ends of the four pulmonary veins, 

 forming a pouch posteriorly between the veins of the right 

 and left sides. The part of the superior vena cava within the 

 pericardium is also invested by it. 



The serous layer forms a reduplicature above and in front of 

 the root of the left lung, enclosing the hbrous remains of the 

 left superior vena cava ; it reaches from the left superior inter- 

 costal vein downwards to the side of the left auricle, where it 

 joins the serous investment round the left upper pulmonary 

 vein. This reduplicature is known as the vestigial fold of 

 Marshall. 



THE HEART. 



The heart is a hollow muscular organ enclosed in the 

 pericardium, and having an irregular conical shape. It is 

 attached at its base to the great bloodvessels, being otherwise 

 free within the pericardial sac. 



Position. The heart is placed obliquely, the base being 

 directed upwards, backwards, and to the right; the apex 

 downwards, forwards, and to the left. The apex corresponds 

 to a point in the 5th left intercostal space 3^ inches from the 

 mid-line. 



The Limits of the Heart. 



Superior. Line from lower border of 2nd left, to upper 

 border of 3rd right costal cartilage. 



Inferior. Line from yth right chondro-sternal articulation to 

 apex. 



Right side. Line drawn nearly vertically i inches from 

 mid-line of sternum, from upper to lower limit. 



Left side. Line from lower border of 2nd left costal cartilage, 

 i inch from sternum, downwards and to the left to apex. 



Position of the Valves. 



Pulmonary. Opposite upper border of 3rd left costal carti- 

 lage near sternum. 



Aortic. Opposite left of sternum, on level with lower 

 border of 3rd costal cartilage. 



Tricuspid. Opposite right of sternum, on level with 4th 

 intercostal space 



