270 THE LUNGS. 



septum. Upon the inner surface, somewhat above the middle of the 

 king, and considerably nearer to the posterior than the anterior border, 

 is the root, where the bronchi and great vessels join the lung. 



Each lung is divided into two lobes by a long and ^qq]) fissure, which 

 commences upon the posterior border, about three inches from the apex, 

 and extends obliquely downwards and forwards to the anterior edge, pene- 

 trating from the outer surface to wdthin a short distance of the root. 

 The tipper lode is the smaller, and is conical, with an oblique base, whilst 

 the lower is quadrilateral. In the right lung a second and shorter 

 •fissure runs forwards and upwards from the principal fissure to the 

 anterior edge, and marks off a small portion, or middle lode, from the 

 lower part of the upper lobe. The left lung has no such middle lobe, l)ut 

 presents a deep notch in its anterior border, into which the apex of the 

 heart (enclosed in the pericardium) is received. Besides these ditfer- 

 ences the right lung is shorter than the left, owing to the diaphragm 

 rising higher on the right side to accommodate the liver, whilst the left 

 lung is the narrower, owing to the heart and pericardium encroaching 

 on the left half of the thorax. On the whole, however, as is seen on a 

 comparison of their Aveights, the right is the larger of the two lungs. 



At the summits and posterior borders the extent of the lungs cor- 

 responds with that of the pleural sacs which contain them, but in front 

 and below the relation is variable, inasmuch as the anterior margins 

 pass forwards most completely between the mediastinal and costal 

 pleura during inspiration, and retire to a variable degree from between 

 them in expiration ; and in like manner the inferior margins descend, 

 during inspiration, between the costal and diaphragmatic pleurjB ; 

 probably at no time do they ever descend completely to the line of 

 reflection between those membranes. 



Weight, Dimensions, and Capacity. — The lungs vary much in 

 size and weight according to the quantity of blood, mucous, or serous 

 fluid they may happen to contain, which is greatly influenced by the 

 circumstances immediately preceding death, as well as by other causes. 

 The weight of both lungs together, as generally stated, ranges from 

 30 to 48 ounces, the more prevalent weights being found between 36 

 and 42 ounces. The proportion borne by the right lung to the left 

 is nearly that of 22 ounces to 20, taking the combined weight of the 

 two at 42 ounces. The lungs are not only absolutely heavier in the 

 male than in the female, but appear to be heavier in proportion to 

 the weight of the body. The general ratio between the weight of the 

 lungs and body, in the adult, fluctuates, according to the estimate of 

 Krause, between one to thirty-five and one to fifty. 



The following tables, deduced from Reid's and Hutchinson's observations, show 

 the average weight of the right and left lungs, and of both lungs together, and 

 also the relative weight of the lungs to the body in a certain number of adults 

 of both sexes. 



AVERAGE WEIGHT IN TWENTY-NINE MALES AND TWENTY-ONE 

 FEMALES. — (REID.) 



MALE. FEMALE. 



Right lung . , . .24:02 17 oz. 



Left lung . . . . 21 oz 15 oz. 



45 oz. 32 oz. 



