THE PERICARDIUM. 



715 



Above, as has been stated, the parietal layer extends upward some distance upon 

 the proximal portions of the systemic and pulmonary aortae before passing over into the 

 visceral layer, but the amount to which the two vessels are invested differs considerably. 

 If the parietal layer be cut away along the line at which it becomes continuous with 

 the visceral layer, two distinct lines will be found indicating its attachments. One of 

 these surrounds the two aortae (Fig. 654), which are united by connective tissue, and 

 extends upward upon the systemic aorta to a point a little below the origin of the 

 innominate artery, a level which corresponds very nearly with the upper border 

 of the second costal cartilage; upon the pulmonary aorta (artery) the line does not 

 rise quite so high, reaching to .a point a little below where the vessel divides into 

 the right and left pulmonary arteries. The other line of attachment is much more 

 extensive and complicated (Fig. 655). Starting from its attachment to the left 



Fig. 676. 



Scalenus amicus muscle 



Thyroid body 

 Vagus nerve 



Clavicle 

 R. com. carotid art., cut 

 Int. mammary artery 



I . costal cartilage 



Innominate 

 artery 

 Sup. vena cava 



Right phrenic 

 nerve 



Mesial surface of 

 right lung 



Stemo-thyroid muscle 

 Sterno-hyoid muscle 

 Stemo-cleido-mastoid muscle 



Right subclavian artery 



Trachea 



I. costal cartilage 



Left phrenic nerve 



Anterior border 



of lung 

 Mesial surface 



of lung 



Pericardial sac 



Diaphragm, central tendon 



Recti muscles 



Anterior thoracic wall has been partly removed, leaving left half of sternum and some 

 ribs in place ; lungs have been drawn aside to expose pericardial sac. 



pulmonary veins, upon which it ascends for a short distance, it passes directly across 

 the posterior surface of the left auricle to the base of the right pulmonary veins, and 

 is thence continued downward to surround the vena cava inferior close to its entrance 

 into the right auricle. Thence it passes upward to regain the right pulmonary veins, 

 and is then continued around the vena cava superior, upon which it rises to a height 

 of about 3 cm. It then passes towards the left over the posterior surface of the 

 auricles to reach the starting-point at the left pulmonary veins. 



The existence of these two separate lines of attachment is due to a diflference in 

 the arrangement of the visceral and parietal layers in the interval between the aortae 

 and the anterior surface of the auricles. The parietal layer passes directly across 

 from the aortae to the auricles, while the visceral layer forms an investment for the 

 vessels, extending downward to their origin from the ventricles, and is thence 



