DISSECTION OF THE BACK AND THORAX. 107 



the lung has not. been injured, it can by this means be restored to 

 its natural position, and the student should then observe the area 

 of pericardium which is left uncovered at the notch in the lower 

 border. The right side of the chest may next be opened, making 

 the same incisions as on the left. On raising the base of the right 

 lung from the diaphragm, its supernumerary lobe will be seen, and 

 also the posterior vena cava and right phrenic nerve invested by the 

 special fold of pleura. The right lung may then be inflated, and the 

 extent of 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 lungs, with 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 pulmonary 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 pure 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 bronchial 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 examination of the pericardium. It is best examined from the 

 left side, and will be sufficiently exposed by hooking the left lung 

 towards the spine. 



