FORM AND SITUATION OF THE LUNGS. 895 



The outer surface of the lung, which moves upon the thoracic parietes, is 

 smooth, convex, and of great extent, corresponding with the arches of the 

 ribs and cost.tl cartilages. It is of greater depth behind than in front. The 

 posterior border is obtuse or rounded, and is received into the deep groove 

 formed by the ribs at the side of the vertebral column ; measured from above 

 downwards, it is the deepest part of the lung. The anterior border is thin 

 and overlaps the pericardium, forming a sharp margin, which touches the sides 

 of the anterior mediastinum, and, opposite the middle of the sternum, is 

 separated during inspiration from the corresponding margin of the opposite 

 lung only by the two thin and adherent layers of the mediastinal septum. 

 The inner surface is concave, and in part adapted to the convex pericardium. 

 Upon this surface, somewhat above the middle of the lung, 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 traversed by a long and deep 

 fissure, which is directed from above and behind, downwards and forwards. 

 It commences upon the posterior border of the lung, about three inches from 

 the apex, and extends obliquely downwards to the anterior and inferior 

 angle, penetrating from the outer surface to within some inches of the root 

 of the organ. The upper lobe, the portion of lung which is situated above this 

 fissure, is smaller than the portion below, and is shaped like a cone with an 

 oblique base, whilst the lower and larger lobe is more or less quadrilateral. 

 In the right lung there is a second and shorter fissure, which runs forwards 

 and upwards from the principal fissure to the anterior margin, thus marking 

 off a third small portion, or middle lobe, which appears like an angular piece 

 separated from the anterior and lower part of the upper lobe. The left lung, 

 which has no such middle lobe, presents a deep notch in its anterior border, 

 into which the apex of the heart (enclosed in the pericardium) is received. 

 This notch is formed by the rapid retreat of the anterior margin of the upper 

 lobe from the middle line, opposite the lower half of the sternum ; while in- 

 ferior ly a tongue-like process of the lower lobe usually projects slightly inwards 

 towards the middle line. Besides these differences in form which distinguish 

 the lungs, it is to be noted that the right lung is shorter, but at the same 

 time wider, than the left, the perpendicular measurement of the former being 

 less, owing to the diaphragm rising higher on the right side to accommodate 

 the liver, whilst the breadth of the left lung is narrowed, 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 weights, the right is the larger 

 of the two lungs. 



At the apices and posterior borders the extent of the lungs accurately cor- 

 responds with that of the pleural sacs which contain them, but at the anterior 

 and inferior margins it is not so : 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 pleurae, while 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, mucus, or serous fluid they may 

 happen to contain, which is greatly influenced by the circumstances im- 

 mediately preceding death, as well as by other causes. The weight of both 

 lungs together, as generally stated, ranges from thirty to forty-eight ounces, 

 the more prevalent weights being found between thirty-six and forty-two 

 ounces. The proportion borne by the right lung to the left is nearly that of 



