This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The apex of the lung has its highest point opposite the posterior extremity of the first rib. It then follows the plane of the top of the first rib down to the sternoclavicular joint, immediately above the junction of the cartilage of the first rib with the sternum. The anterior end of the first rib is 5 cm. lower than the posterior. The upper edge of the clavicle is 2.5 cm. or one inch, above the anterior end of the first rib and 2.5 cm. below the head of the first rib, hence the apex of the lung rises 2.5 cm. (1 in.) above the clavicle, and it lies behind its inner fourth. This distance will vary in different individuals with the obliquity of the ribs. The more oblique the ribs the greater will be the distance between the level of the top of the clavicle and that of the neck of the first rib.
From the sternoclavicular joint the borders of the lungs pass downward and inward until they almost or quite touch in the median line at the angle of Ludwig opposite the second costal cartilage. They continue downward almost in a straight line until opposite the fourth costal cartilage, where they begin to diverge. The border of the right lung proceeds downward and begins to turn outward opposite the sixth cartilage.
The left lung on reaching the level of the fourth costal cartilage curves outward and downward across the fourth interspace to a point about 2.5 cm. to the inner side of the nipple in the fourth interspace. From this point it goes downward and inward across the fifth rib and interspace to the top of the sixth rib about 3 cm. to the inner side of the nipple line. This isolated tip of lung just above the sixth rib over the apex beat of the heart is called the lingula.
The lower edge of the lung varies in different individuals and in the same individual according to the amount of inflation. In quiet respiration it is about opposite the sixth cartilage and rib from the sternum to the mammary line, opposite the eighth in the midaxillary line, the tenth in the scapular line, and the eleventh near the vertebrae.
The left lung has one fissure and two lobes, an upper and a lower.
The right lung has two fissures and three lobes, an upper, a middle, and a lower.
The fissure of the left lung begins above and posteriorly opposite the root of the spine of the scapula; this is level with the fourth rib and third dorsal spine. It passes downward and forward, ending at the sixth rib in the parasternal line. It crosses the fourth in the midaxillary line. The lower lobe of the right lung is of the same size as that of the left side. The lung above it is divided into a middle and upper lobe. The main fissure of the right lung corresponds in its course almost exactly with that of the left lung. It begins above and posteriorly at the root of the spine of the scapula and passing downward crosses the fourth rib in the midaxillary line and ends at the sixth rib in the mammary line (instead of the parasternal line as in the left).
The subsidiary fissure of the right lung leaves the main fissure at the posterior axillary line opposite the fourth rib and follows this rib in an almost horizontal direction to its junction with the sternum.
In order to recognize and appreciate the changes which occur in the lungs in lobar pneumonia it is necessary to know the outlines and limits of the various lobes of the lungs. A knowledge of the exact course of the fissures of the lungs is not only necessary to outline the lobes, but it is of service in the diagnosis of pleural effusions. These effusions often are limited to certain localized areas instead of being general.
Pleurisy may affect the lung bordering the fissures. When such is the case, the effusion, serous or purulent, may be in the fissure itself and embrace but little of the general pleural cavity. Dry taps from failure to hit the purulent or serous collection are not infrequent, and the possibility of its being interlobar should be borne in mind.
From what has been said it follows that a knowledge of the extent and outlines of the lungs and of the location and course of the fissures is essential to the proper diagnosis and treatment of affections of both the lungs and pleurae.
The extent of the lungs is determined in the living by percussion. The apex of the lungs forms an oblique plane running upward and backward from just below the lower edge of the inner extremity of the clavicle to the neck of the first rib above and posteriorly. The level of these two points will vary according to the inclination of the ribs, which in turn is influenced by the direction (vertical) of the spine. Ordinarily the distance is 5 cm. (2 in.). It may be even as much as 7 or 8 cm. The top edge of the clavicle passes across the middle of this distance so that the top of the lung is about 2.5 cm. (1 in.) above the clavicle. The highest point of the lung is not in the middle of the space enclosed by the first rib, but is at its posterior border, at the neck of the first rib.
In percussing, one should not strike directly backward but both downward and backward.
If the patient is standing erect the first rib will slope downward and forward at an angle of 65 degrees, or more, with a vertical line. The spine will slope downward and backward from the same vertical line in a normally straight back about 20 degrees.
In people with straight backs and flat chests (often seen in phthisis), the sloping downward of the ribs is marked; in those with rounded backs the chest is apt to be round, as in emphysema, and then the ribs are more horizontal.
Another point to be noticed is the lateral extent of the apex of the lung in relation to the length of the clavicle. The lung does not extend farther out on the clavicle than one-fourth its length. The clavicular origin of the sternomastoid muscle extends out one-third of the length of the clavicle, so that the lung is behind the clavicular origin of the sternomastoid and care should be taken not to percuss too far out. If the finger is laid in the supraclavicular fossa in percussion it should be pressed downward and inward, not backward.
Posteriorly the scapula rises to the second rib and its spine has its root opposite the fourth rib or spinous process of the third thoracic vertebra. Therefore a small portion of the lung is above the upper edge of the scapula and percussion in the supraspinous fossa gives a clear resonant note.
Behind the middle of the first piece of the sternum passes the trachea, crossed by the left innominate vein. The trachea of course contains air; the lungs slope inward from the sternoclavicular joints to meet nearly or quite in the median line and so continue to the level of the fourth rib; hence it follows that the percussion note on the sternum nearly down to this point is resonant and if it be found to be dull one should look for an aneurismal or other tumor which is displacing or covering the lungs and trachea at this point and thereby subduing their resonance.
Fig. 217. - Formalin-hardened body, showing the right lung collapsed and compressed by a large pleural effusion.
Below the fourth rib the area of the absolute heart dulness becomes evident. This will be alluded to in describing that organ later on.) In performing abdominal operations, as those involving the gall-bladder and kidney, the surgeon may be tempted to prolong his incision upward into the lower edge of the chest-walls, and it is necessary to know how far he can proceed without opening the pleural cavity. This necessitates his knowing how far from the lower edge of the chest the pleura lies. It reaches to the seventh rib in the mammary line, the ninth in the axillary line, and the twelfth posteriorly, extending to its extreme lower edge.
In the axillary line the pleura is about 6 cm. (2§ in.) away from the edge of he thorax. This distance gets less as one proceeds forward to the sternum and backward toward the spine.
In emphysema the lung, being distended, occupies more nearly the outlines of the pleura and its area of resonance is increased. In pleural effusion it is compressed and even sometimes collapsed. As it shrinks it recedes inward and backward and is pushed from the chest-wall by the layer of fluid (Fig. 217). The pressure of the fluid within causes the intercostal spaces to be obliterated and sometimes even to bulge instead of being depressed. As the expansion of the lung is prevented, the chest does not move on the affected side, or expand with the respiration, as it does on the healthy side. This can be demonstrated by measuring the two sides of the chest. At the end of expiration the affected side will be from 1 to 3 cm. greater in circumference than the healthy one. If the pleural effusion is on the right side it may push the heart to the left and raise its apex beat and cause it to pulsate beyond the nipple line and even in the axilla. If it is on the left side the costomediastinal sinus (page 196) becomes distended with fluid or plastic lymph and this obscures or conceals the heart's impulse. If the effusion is very large the heart is pushed over toward the right and its apex beat is seen in the third or fourth interspace on the right side even so far over as the mammary line.
Should the effusion be purulent it may perforate the chest-wall, or open into the pericardium anteriorly, the oesophagus posteriorly, and into the stomach or peritoneal cavity below. If it perforates the chest-wall it usually does so anteriorly between the third and sixth interspaces, most often in the fifth.