Surface markings of the more important thoracic contents (Figs 2–4)

The Trachea

The trachea commences in the neck at the level of the lower border of the cricoid cartilage (COMPLETE RING OF CARTILAGE AROUND THE TRACHEA (C6)) and runs vertically downwards to end at the level of the sternal angle of Louis (T4/5), just to the right of the mid-line, by dividing to form the right and left main bronchi. In the erect position and in full inspiration the level of bifurcation (THE SPLITTING OF A MAIN BODY INTO TWO PARTS) is at T6.

The Pleura

The cervical pleura can be marked out on the surface by a curved line drawn from the sternoclavicular joint (JOINT BETWEEN THE CLAVICLES AND THE STERNUM) to the junction of the medial and middle thirds of the clavicle; the apex of the pleura is about 2.5cm above the clavicle. This fact is easily explained by the oblique slope of the first rib. It is important because the pleura can be wounded (with consequent pneumothorax) by a stab wound — and this includes the surgeon’s knife and the anaesthetist’s needle—above the clavicle.

The lines of pleural reflexion pass from behind the sternoclavicular joint on each side to meet in the midline at the 2nd costal cartilage (the angle of Louis). The right pleural edge then passes vertically downwards to the 6th costal cartilage and then crosses:

•◊◊the 8th rib in the midclavicular line;

•◊◊the 10th rib in the midaxillary line;

•◊◊the 12th rib at the lateral border of the erector spinae (VERTEBRAL MUSCLES).

On the left side the pleural edge arches laterally at the 4th costal cartilage and descends lateral to the border of the sternum, due, of course, to its lateral displacement by the heart; apart from this, its relationships are those of the right side.

The pleura actually descends just below the 12th rib margin at its medial extremity (LIMIT) — or even below the edge of the 11th rib if the 12th is unusually short; obviously in this situation the pleura may be opened accidentally in making a loin incision to expose the kidney, perform an adrenalectomy or to drain a subphrenic abscess.

The Lungs

The surface projection of the lung is somewhat less extensive than that of the parietal pleura (OUTER LINING OF THE THORAX) as outlined above, and in addition it varies quite considerably with the phase of respiration. The apex of the lung closely follows the line of the cervical pleura (THE DOME-SHAPED LAYER OF PARIETAL PLEURA LINING THE CERVICAL EXTENSION OF THE PLEURAL CAVITY) and the surface marking of the anterior border of the right lung corresponds to that of the right mediastinal pleura (SECTION OF THE PARIETAL PLEURA).

On the left side, however, the anterior border has a distinct notch (the cardiac notch) which passes behind the 5th and 6th costal cartilages. The lower border of the lung has an excursion of as much as 5–8cm in the extremes of respiration, but in the neutral position (MIDWAY BETWEEN INSPIRATION AND EXPIRATION) it lies along a line which crosses the 6th rib in the midclavicular line (VERTICAL LINE CROSSING THROUGH THE CLAVICLE), the 8th rib in the midaxillary line (PERPENDICULAR LINE DRAWN DOWNWARD FROM THE APEX OF THE AXILLA), and reaches the 10th rib adjacent (NEIGHBOURING) to the vertebral column posteriorly (FROM THE BACK).

The oblique fissure, which divides the lung into upper and lower lobes, is indicated on the surface by a line drawn obliquely downwards and outwards from 2.5cm lateral (ADJACENT) to the spine of the 5th thoracic vertebra to the 6th costal cartilage about 4cm from the midline. This can be represented approximately by abducting the shoulder to its full extent; the line of the oblique fissure then corresponds to the position of the medial (IN THE CENTER) border of the scapula.

The surface marking of the transverse fissure (separating the middle and upper lobes of the right lung) is a line drawn horizontally along the 4th costal cartilage and meeting the oblique fissure where the latter crosses the 5 th rib.

The heart

The outline of the heart can be represented on the surface by the irregular quadrangle bounded by the following four points (Fig. 4):

1◊◊the 2nd left costal cartilage 12mm from the edge of the sternum;

2◊◊the 3rd right costal cartilage 12mm from the sternal edge;

3◊◊the 6th right costal cartilage 12mm from the sternum;

4◊◊the 5th left intercostal space 9cm from the midline (corresponding to the apex beat).

The left border of the heart (indicated by the curved line joining points 1 and 4) is formed almost entirely by the left ventricle (the auricular appendage (ADDITION) of the left atrium peeping around this border superiorly), the lower border (the horizontal line joining points 3 and 4) corresponds to the right ventricle and the apical part of the left ventricle; the right border (marked by the line joining points 2 and 3) is formed by the right atrium (see Fig. 24a).

A good guide to the size and position of your own heart is given by placing your clenched right fist palmar surface down immediately inferior (LOWER, UNDER) to the manubriosternal junction.

 Note that the heart is about the size of the subject’s fist, lies behind the body of the sternum (therefore anterior to thoracic vertebrae 5–8), and bulges over to the left side. The surface markings of the vessels of the thoracic wall are of importance if these structures are to be avoided in performing aspiration of the chest.

The internal thoracic (internal mammary) vessels run vertically downwards behind the costal cartilages half an inch from the lateral border of the sternum. The intercostal vessels lie immediately below their corresponding ribs (the vein above the artery) so that it is safe to pass a needle immediately above a rib, dangerous to pass it immediately below (see Fig. 8).