LIMITS OF THE LUNGS. 1 77 



so that the lower part becomes the wider of the two. The right half of the chest is 

 usually slightly larger than the left half, owing to the greater development of the 

 muscles on that side. The long diameter of the chest from the clavicle to the 

 margin of the lowest rib varies very much. 



The transverse diameter in man, above and below, is 25 to 26 centimetres (9*7 

 to 10*1 inches), in females 23 to 24 centimetres (8 '9 to 9*2 inches) ; above the 

 nipple it is 1 centimetre more. The antero-posterior diameter (distance of 

 aDterior chest- wall from the tip of a spinous process) in the upper part of the chest 

 is = 17 (6'6 inches), in the lower 19 centimetres (7*4 inches). Valentin found 

 that in a man, during the deepest inspiration, the chest on a level with the 

 groove in the heart was increased about ^ to \ \ while Sibson estimates the increase 

 at the level of the nipple to be ^. 



Thoracometer. In order to obtain a knowledge of the degree of movement rising or fall- 

 ing of the chest-wall during respiration, various instruments have been invented. The 

 thoracometer (fig. 141) measures the elevation in different parts of the sternum. It consists of 

 two metallic bars placed at right angles to each other ; one of them, A, is placed on the 

 vertebral column. On B there is placed a movable transverse bar, C, which carries on its 

 free end a toothed rod, Z, directed downwards. The lower end x>f this rod is provided with 

 a pad which rests on the sternum, while its toothed edge drives a small wheel, which moves 

 an index, whose excursions are indicated on a circle with a scale attached to it. 



The Cyrtometer of Woillez consists of a brass chain of movable links, to be applied in a definite 

 direction to part of the chest-wall, e.g., transversely on a level with the nipple, or vertically 

 upon the mammillary or axillary lines anteriorly. There are freely movable links at two parts, 

 which permit the chain to be easily removed, so that as a whole it still retains its form. The 

 chain is laid upon a sheet of paper, and a line drawn with a pencil around its inner margin 

 gives the form of the thorax (fig. 140). [A lead wire answers the same purpose.] 



Limits of the Lungs. The extent and boundaries of the lungs are ascertained 

 in the living subject by means of percussion, which consists in lightly tapping the 

 chest- wall by means of a hammer (percussion-hammer). A small ivory or bone 

 plate or pleximeter, held in the left hand, is laid on the chest, and the hammer is 

 made to strike this plate, whereby a sound is emitted, which sound varies with the 

 condition of the subjacent lung-tissue. Whenever the lung-substance in contact 

 with the chest- wall contains air, a clear resonant tone or sound such as is obtained 

 by striking a vessel containing air, a clear percussion-sound is obtained. Where 

 the lung does not contain air, a dull sound like striking a limb is obtained. 

 If the parts containing air be very thin, or only partially filled with air, the 

 sound is " muffled." 



Fig. 142 indicates the relation of the lungs to the anterior surface of the chest. 

 The apices of the lungs reach 3 to 7 centimetres (1*1 to 2 '7 inches) above the 

 clavicles anteriorly, while posteriorly they extend from the spines of the scapula 

 as high as the seventh spinous process. The lower margin of the right lung in the 

 passive position (moderate expiration) of the chest, commences at the right margin 

 of the sternum at the insertion of the sixth rib, runs under the right nipple, nearly 

 parallel to the upper border of the sixth rib, and descends a little in the axillary 

 line, to the upper margin of the seventh rib. On the left side (apart from the 

 position of the heart), the lower limit reaches as far down anteriorly as the right. 

 In fig. 142 the line a, t, b shows the lowest limit of the passive lungs. Posteriorly 

 both lungs reach as far down as the tenth rib. During the deepest inspiration, the 

 lungs descend anteriorly as far as between the sixth and seventh ribs, and posteriorly 

 to the eleventh rib whereby the diaphragm is separated from the thoracic wall 

 (fig. 143). During the deepest expiration, the lower margins of the lungs are 

 elevated almost as much as they descend during inspiration. In fig. 142, m, n 

 indicates the margin of the right lung during deep inspiration ; h, I, during deep 

 expiration. [The part of the chest-wall covered by the costal pleura is considerably 

 larger than the circumference of the lung. This is specially marked at the lower 

 margin of the lung, and where the left lung is incised over the heart. In these 



M 



