458 



THE BLOOD-VASCULAR SYSTEM. 



Structure of the Pericardium. The pericardium is a fibro-serous membrane, 

 and consists, therefore, of two layers, an external fibrous and an internal serous. 



The fibrous layer is a strong, dense membrane. Above, it surrounds the great 

 vessels arising from the base of the heart, on which it is continued in the form 

 of tubular prolongations which are gradually lost upon their external coat, the 

 strongest being that which encloses the aorta. The pericardium may be traced 

 over these vessels, to become continuous with the deep layer of the cervical fascia. 

 In front the pericardium is connected to the posterior surface of the sternum by 

 two fibrous bands, the superior and inferior sterno-pericardiac ligaments, the upper 



Left subclariaii artery 

 E'njlit pulmonary artery. 



Left common 

 carotid artery. 



Kiibclavian artery. 



ftiyht common 

 carotid artery. 



Inferior thyroid 

 vein. 



-Vena azyyos 

 major. 



Right pulmonary 

 reins. 



FIG. 274. Pericardium, from behind. (From the same preparation as the preceding figure.) 



passing to the manubrium, and the lower to the ensiform cartilage. On each side 

 of the ascending aorta it sends upward a diverticulum : the one on the left side, 

 somewhat conical in shape, passes upward and outward, between the arch of the 

 aorta and the pulmonary artery, as far as the ductus arteriosus, where it termi- 

 nates in a crecal extremity, which is attached by loose connective tissue to the 

 obliterated duct (Fig. 273). The one on the right side passes upward and to the 

 right, between the ascending aorta and vena cava superior, and also terminates in 

 a caecal extremity. Below, the fibrous layer is attached to the central tendon of 

 the Diaphragm, and on the left side to its muscular fibres. 



The vessels receiving fibrous prolongations from this membrane are the aorta, 

 the superior vena cava, the right and left pulmonary arteries, and the four pulmo- 



