478 



DISSECTION OF THE THORAX. 



left in size 

 and rela- 

 tions. 



Remove the 

 lungs. 



Take away 

 heart and 

 pericardium. 



Surface of 

 lung is 

 smooth ; 

 is marked 

 by lobules 

 and small 

 cells. 



Colour 

 varies with 

 age. 



Accidental 

 colour. 



Consistence. 



Crepitation, 



and elasti- 

 city. 



Specific 

 gravity, 



and weight 

 of the lung. 



Lung con- 

 sists of 

 lobules, and 

 these of air- 

 cells. 



level with, the fifth dorsal vertebra, behind the upper cava and the 

 right pulmonary artery ; and the azygos vein arches above it. 



The left bronchus is about two inches long, and reaches to the 

 level of the sixth dorsal vertebra. It is directed obliquely down- 

 wards below the arch of the aorta, and crosses behind the corre- 

 sponding pulmonary artery. It lies in front of the oesophagus and 

 descending thoracic aorta. 



Dissection. The lungs are now to be removed from the body 

 by cutting through the bronchi and the small vessels of the root. 



The remains of the heart and pericardium are then to be taken 

 away ; the inferior cava is to be divided, and the pericardium is to 

 be detached from the surface of the diaphragm : in removing the 

 pericardium, the dissector should be careful not to injure the 

 structures contained in the interpleural space in front of the spine. 



PHYSICAL CHARACTERS OF THE LUNG. The surface of the lung 

 is smooth and shining, and is invested by the pleura. Through the 

 serous covering the mass of the lung may be seen to be divided 

 into small irregularly shaped pieces or lobules. On looking closely 

 at it, when a piece of pulmonary pleura is pulled away from its 

 substance, minute cells will be perceived in it. 



The tint of the lung varies with age. In infancy the colour is a 

 pale red ; but in the adult the texture becomes greyish, and presents 

 here and there dark grey spots or lines of pigment, the shade of 

 which deepens with increasing age, and becomes even black in old 

 people. After death, the colour of the posterior border may be 

 bluish-black from the accumulation of blood. 



To the touch the lung is soft and yielding, and on a section the 

 pulmonary substance appears like a sponge ; but the lung which 

 is deprived of air by pressure has a tough leathery feel. Slight 

 pressure with the thumb and finger drives the air from the con- 

 taining spaces through the pulmonary structure, and produces the 

 noise known as crepitation. If the lung contains serum or mucus, 

 a frothy red fluid will run out when it is cut. 



The texture of the lung is very elastic, this elasticity causing the 

 organ to contract when the thorax is opened, and to expel air that 

 may be blown into it. 



The specific gravity of the lung varies with the conditions of 

 dilatation and collapse, or of infiltration with fluid. When the 

 pulmonary substance is free from fluid, and filled with air, it floats 

 in water ; but when it is quite deprived of air it is slightly heavier 

 than water, and therefore sinks. The weight of the lung is 

 influenced greatly by the quantity of foreign material contained in 

 its texture ; ordinarily it ranges from sixteen to twenty-four ounces, 

 the right lung being about two ounces heavier than the left. In 

 the male the lungs are larger, and, together, they are about twelve 

 ounces heavier than in the female. 



OBVIOUS STRUCTURE OF THE LUNG-. The substance of the lung 

 is composed of small polyhedral masses or lobules, which are hollow, 

 and again subdivided into minute vesicles called the air-cells. The 

 lobules are visible as little polygonal areas, marked by the lines of 



