Topography Of The Lungs (Posterior View)
The apex of the lung extends as far superiorly as the vertebral end of the ﬁrst rib and therefore as high as the ﬁrst thoracic vertebra. From there, the lung extends inferiorly as far as the diaphragm, with the base of the lung resting on the diaphragm and ﬁtted to its superior surface. Because of the diaphragm’s domed shape, the level of the highest point on the base of the right lung is about at the eighth to ninth thoracic vertebrae. The highest point on the base of the left lung is a fraction of an inch lower. From these high points, the bases of the two lungs follow the curves of the diaphragm to reach the levels described earlier for the inferior borders of the lungs.
The highest point on the oblique ﬁssure of the two lungs is on their posterior aspects, at about the level of the third to fourth thoracic vertebrae, a little over 1 inch from the midline.
If the arm is raised over the head, the vertebral border of the scapula approximates the position of the oblique ﬁssure of the lung. If the shoulder is brought forward as far as possible, the scapula is carried laterally, so that the area in which auscultation can be satisfactorily carried out on the posterior aspect of the chest is signiﬁcantly widened.
The parietal pleura is separated from the visceral pleura by a potential space (the pleural cavity), which under normal circumstances contains only a minimal amount of serous ﬂuid. Caudal to the inferior margin of the lung, the costal parietal pleura is in contact with the diaphragmatic parietal pleura, forming the costo- diaphragmatic recess (costophrenic sulcus). This allows for the caudal movement of the inferior margin of the lung on inspiration.
Under abnormal circumstances, the pleural cavity may contain air, increased amounts of serous ﬂuid, blood, or pus. The accumulation of a signiﬁcant amount of any of these in the pleural cavity compresses the lung and causes respiratory difﬁculties.
The diaphragm separates the base of the left lung from the fundus of the stomach and the spleen. Because of this relationship, if the stomach is distended by food or gas, it may push the diaphragm upward and embarrass respiratory activity.
The diaphragm similarly separates the base of the right lung from the liver, which, if enlarged, elevates the diaphragm and pushes against the lung, possibly
limiting its expansion. A hepatic abscess may rupture through the diaphragm to involve the related pleural cavity and lung.
In this illustration, the lungs are shown in relation to the bony thorax, scapula, and diaphragm, but overlying the structures shown are the deep and superﬁcial muscles of the back in addition to the superﬁcial fascia and skin.