THE PERICARDIUM 



551 



in the portal vein passes through two sets of capillary vessels (1) those in the 

 spleen, pancreas, stomach, etc., and (2) those in the liver. 



Speaking generally, the arteries may be said to contain pure and the veins im- 

 pure blood. This is true of the systemic but not of the pulmonary vessels, 

 since it has been seen that the impure blood is conveyed from the heart to the 

 lungs by the pulmonary arteries, and the pure blood returned from the lungs to 

 the heart by the pulmonary veins. Arteries, therefore, must be defined as vessels 

 which convey blood from the heart, and veins as vessels which return blood to 

 the heart. 



The heart and lungs are contained within the cavity of the thorax, the walls of 

 which afford them protection (Fig. 410). The heart lies between the two lungs, 

 and is there enclosed within a seromembranous bag, the pericardium, while each 

 lung is invested by a serous membrane, the pleura. The skeleton and cavity of 

 the thorax were described on page 154. 



VERTEBRO- 



PERICAROIAL 



LIGAMENTS 



SUPERIOR 

 VENA CAVA 



INTERIOR 

 VENA CAVA 



PHRENO- 



PERICARDIAL 



LIGAMENTS 



SUPERIOR STEHNO- 

 PERICARDIAL LIG- 

 AMENTS 



ANTERIOR 

 SURFACE OF 

 PERICARDIUM 



XIPHO- 



PERICARDIAL 



LIGAMENTS 



FIG. 411. Ligaments of the pericardium. (Modified from Teutleben.) Right lateral view, showing the right 

 vertebropericardial ligaments, the right phrenopericardial, and the superior and inferior sternopericardial 

 ligaments. (Poirier and Charpy.) 



THE PERICARDIUM. 



The pericardium (Figs. 411 and 412) is a conical seromembranous sac, placed 

 in the middle mediastinum. In this sac the heart and the commencement of the 

 great vessels are contained. It is placed behind the sternum and the cartilages 



