DISSECTION OF THE BACK AND THORAX. 105 



pericardium left uncovered by lung on this side should be observed. 

 Thereafter, the lung should be reflected towards the spine, and the 

 pleura should be stripped off its root. The vessels, nerves, and bronchus 

 should be isolated by teasing and scraping, rather than by cutting. 



The Root of the Lung, it will be observed, is placed behind the upper 

 part of the heart ; and it is composed of the bronchus, bloodvessels, 

 lymph-vessels, and nerves of the lung, Avith some connective-tissue. 

 The bronchus enters each root in front and above ; the pulmonary veins 

 enter behind ; and the pulmonary artery enters in front of the veins. 



Vessels, Two sets of vessels pass to and from the lung at the root, 

 viz., the pulmonary artery and veins, and the bronchial artery and vein. 



The Pulmonary Artery is the enormous vessel carrying impure (venous) 

 blood from the right ventricle to be purified in the capillaries on the 

 air-cells of the lung. It will be recognised by the thickness of its wall. 

 The lyubnonary veins bring the purified (arterial) blood back from the air- 

 cells, and discharge it into the left auricle. They form at the root of 

 the lung from two to four trunks, which are extremely short, especially 

 on the left side. The pulmonary vessels are the functional vessels of 

 the lung. 



The Bronchial Artery is a slender vessel entering the lung on the 

 bronchus. It carries nutritive or pm-e blood to the lung structure, and 

 may therefore be termed the nutrient artery of the lung. The blood which 

 it carries is led out of the lung by the hronchial vein, which joins the 

 coronary sinus of the heart. 



The Nerves of the lung are derived from the vagus, as will be seen 

 at a later stage. They form a plexus at its root, and pass along the 

 bronchi into its interior. 



Directions. — Both lungs are to be left until the heart and the thoracic 

 vessels and nerves have been examined. Proceed now to the examina- 

 tion of the pericardium. It is best examined from the left side, and 

 Avill be sufficiently exposed by hooking the left lung towards the spine. 



THE pericardium (pLATES 22 AND 26). 



The pericardium is the bag that contains the heart. It occupies a 

 position about the centre of the thorax, and between the right and left 

 layers of the mediastinum. The sac is fibrous in structure, and is lined 

 internally by a serous membrane. Like the organ which it encloses, 

 the pericardium has a conical form, the point of the cone being fixed to 

 the floor of the sternum from about the third chondro-sternal joint to 

 within an inch of the insertion of the diaphragm across the ensiform 

 cartilage. Above the sac is pierced by the large vessels of the heart, and 

 there its fibrous texture blends with the outer coat of the vessels. 

 Its outer surface is overspread by the mediastinal pleura, which can 

 easily be stripped oft". 



