522 



THE BLOOD-VASCULAR SYSTEM 



with the finer branches of the cardiac veins, and also with the general capillaiy network in the 

 heart's waUs. 



The lymphatic vessels of the heart pass chiefly through the anterior mediastinal lymph- 

 nodes into the broncho-mediastinal trunk. (See Section VI.) 



The cardiac nerves, derived from the vagus and the cervical sympathetic, descend into the 

 superior mediastinum, passing in front of and behind the arch of the aorta; they unite in the 

 formation of the superficial and deep cardiac plexuses. The superficial plexus lies above the 

 right pulmonary artery as the latter passes beneath the aortic arch. The deep plexus lies be- 

 tween the trachea and the arch of the aorta, above the bifurcation of the pulmonary trunk. 

 For the connections of the plexuses see section on Nervous System. 



2. THE PERICARDIUM 



The pericardium is a cone-shaped, fibro-serous sac which surrounds the heart 

 and contains a small amount of fluid [liquor pericardii]. Its apex is above at the 

 root of the great vessels, and its base below, adherent to the diaphragm. Its 

 connection with the diaphragm is in part to the central tendon and in part to the 

 muscle, especially on the left side. It consists of an outer fibrous layer and an 

 inner serous layer. The virtual space between the serous pericardium and the 

 epicardium is commonly called the pericardial cavity. 



Fia. 436. 



-Left Posterior View of the Heart to show the Reflections of the Peri- 

 cardium. 



Aortic arch • 



Pulmonary artery 



Left pulm. artery 



Anterior longit. 

 sulcus 



Morgo obtusus 



I 



— ;- Ligamentum 

 arteriosum 



Ligament of left 

 superior cava 



Left atrium 



Oblique sinus of 

 pericardium 



Left inf. pulm. 

 vein 



Coronary sinus 



Vena cava inferior 



The fibrous layer is strong and inelastic, made of interlacing fibres. Its connection with 

 the central tendon of \\u\ diaphragm is intimate, particulnrly in tlie region of the caval opening, 

 but ehsewhere it is attac^hed loosely l)y means of areolar tissue. Above, it is lost on the sheaths 

 of the great vessels, all of wliich receive distinct investments, with the single exception of the 

 inferior vena cava, which pierces it from below. The aorta, superior vena cava, the pulmonary 

 artery, and the four pulm(jnary veins, are all ensheathcd in this maimer. The pericardium is 

 connected above with th(! deep cervical fascia. Two variable bands of fibrous tissue, the 

 sterno-pericardial ligaments |ligg. sterno-pericardiaca|, connect the front of the pericardium, 

 above and below, with the posterior surface of the sternum. 



