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serratus anterior afford reliable guides to the fifth rib. The infra-sternal notch is the guide to the medial end of the seventh costal cartilage. The second and third an costal cartilages are almost horizontal; below this the cartilages ascend with increasing obliquity, that of the sixth being the first to present a distinct angle. Pl The anterior end of the second intercostal space is the widest, while those of the fifth and sixth are very narrow.
The costo-chondral junctions may be indicated, on the surface, by a line drawn from the superior end of the para-sternal line to a point a finger's breadth posterior to the angle of the tenth costal cartilage.
The internal mammary artery crosses behind the medial ends of the superior five intercostal spaces, about half an inch from the edge of the sternum; as it descends it approaches a little nearer to the sternum. The vessel is accompanied by two veins which unite to form a single vein opposite the second interspace.
This artery is occasionally injured in punctured wounds of the chest. At the second or third intercostal space it is easily ligatured through a transverse incision, but at a lower level it is generally necessary to resect a portion of one of the costal cartilages.
THE LUNGS AND PLEURÆ.
The apex of the lung extends upwards into the root of the neck for a distance of one to two inches superior to the anterior extremity of the first rib, and is mapped out by a curved line drawn from the superior border of the sterno-clavicular articulation across the sterno-mastoid to the junction of the medial and intermediate thirds of the clavicle, the highest part of the curve reaching from to 11 in. above the clavicle. The apex of the right lung reaches half an inch higher than that of the left lung. Intimately related to the apex of the cervical pleura are the subclavian artery and the inferior cervical ganglion of the sympathetic.
Both the cervical pleura and the subclavian artery may be injured by one of the fragments in a fracture of the clavicle; the scaleni muscles, however, affording considerable protection to the pleura. In ligaturing the third part of the subclavian artery, care must be taken not to injure the cervical pleura.
To delineate the anterior border of the right lung, draw a line from the superior border of the sterno-clavicular articulation to the centre of the manubrium sterni, and from there vertically downwards, in or slightly to the left of the median plane to the level of the sixth or seventh costal cartilage, or, it may be, even to the infrasternal notch (Fig. 1091).
The anterior border of the left lung is mapped out by a corresponding line as far as the fourth costal cartilage; thence it is directed laterally along the inferior border of the fourth costal cartilage to the para-sternal line; it then passes downwards and slightly laterally across the fourth interspace, and curves medially behind the fifth costal cartilage and fifth interspace to reach the superior border of the sixth costal cartilage in the para-sternal line. The inferior part, therefore, of the anterior surface of the right ventricle is uncovered by lung and gives a completely dull note on percussion; this area is spoken of as the area of "superficial or absolute cardiac dulness."
The level of the inferior border of the lung is practically the same on both sides. it is mapped out by a line extending laterally from the inferior extremity of the anterior border to the sixth costal cartilage in the mid-clavicular line, and thence in a slightly curved direction, with the convexity downwards, across the lateral aspect of the chest to the tenth thoracic spine. This line crosses the eighth rib the mid-axillary line and the tenth rib in the scapular line (Figs. 1091 and 1092)
To indicate the position of the oblique fissure a line is drawn from the second thoracic spine across the interscapular region to the root of the spine of the scapula. and thence downwards and laterally across the infraspinous fossa, to end at the inferior border of the lung opposite the sixth costal cartilage, a little medial to the mammary line. When the arm is raised above the level of the shoulder, and the hand placed on the back of the head, the inferior angle of the scapula is rotated upwards and forwards so that the vertebral margin practically corresponds with the line of the oblique fissure.
The transverse fissure of the right lung is mapped out by drawing a line from the anterior border of the lung, at the level of the fourth costal cartilage, laterally and slightly upwards to join the middle of the oblique fissure.
Pleuræ. The line of reflection of the right pleura from the back of the sternum may be said to correspond to the anterior border of the right lung.
FIG. 1091.-DISSECTION OF A SUBJECT HARDENED BY FORMALIN INJECTION, to show the relations of the two pleural sacs as viewed from the front. The anterior and diaphragmatic lines of pleural reflection are exhibited by black dotted lines, whilst the outlines of the lungs and their fissures are indicated by the blue lines. (From Cunningham.)
On the left side, the pleural reflection corresponds to the anterior border of the left lung as far as the inferior edge of the fourth chondro-sternal junction, from which point it diverges slightly and descends, behind the left border of the sternum, to the sixth costal cartilage (Fig. 1091). It is only occasionally that the anterior extremities of the fifth and sixth interspaces are uncovered by pleura.
The right costo-diaphragmatic reflection (see Figs. 1091 and 1093) is indicated on the surface by a line drawn from the sixth or seventh chondro-sternal junction (sometimes the infrasternal notch) downwards and laterally to a point two inches
vertically above the angle of the tenth costal cartilage; from that point the line is carried, with a slightly downward curve, across the lateral aspect of the chest to the twelfth rib at the lateral margin of the sacro-spinalis; thence it passes below the twelfth rib and reaches the vertebral column at the level of the superior border of the twelfth thoracic spine. The relation of the costo-diaphragmatic reflection to the seventh, eighth, and ninth costal arches may be conveniently expressed by stating that it lies a little in front of the costo-chondral junction of the seventh, opposite that of the eighth, and a
little behind that of the ninth.
The left costo-diaphragmatic reflection is indicated by a line drawn from a point opposite the sixth costal cartilage, a finger's breadth from its junction with the sternum, to a point one and a half inches vertically above the angle of the tenth costal cartilage, and thence to the vertebral column, as on the right side, but at a slightly inferior level.
The costo-diaphragmatic reflection reaches its lowest limit a little behind the mid-axillary line two inches vertically above the tip of the eleventh costal cartilage, a level which may be readily indicated, according to Cunningham, by a point in the mid-axillary line intersected by a horizontal line drawn round the trunk at the level of the lowest part of the extremity of the first lumbar spine (Fig. 1092). The same author localised the level of the diaphragmatic pleural reflection in the mammary line at the point where this line is intersected by another horizontal line at the level of the spine of the last thoracic vertebra.
The relations of the pleura to the twelfth rib are of importance to the surgeon, especially in connexion with operations on the kidney (Figs. 1094 and 1095). When this rib is not abnormally short, the pleural reflection crosses it opposite the lateral border of the sacro-spinalis muscle; hence an incision may be carried FIG. deeply as far as the apex of the angle formed by the twelfth rib and the lateral border of the sacro-spinalis
1093.-LATERAL VIEW OF THE RIGHT PLEURAL SAC IN
A SUBJECT HARDENED BY FORMALIN INJECTION. The blue lines indicate the outline of the right lung, and also the position of its fissures. (From Cunningham.)
without entering the pleura. When, however, the twelfth rib does not reach the lateral border of the sacro-spinalis, an incision carried upwards into the apex of the angle between this muscle and the eleventh rib is certain to wound the pleura (Melsom). It is important, therefore, to count the ribs from above downwards, in order not to mistake the eleventh for the twelfth, when the latter is rudimentary.
Medial to the lateral edge of the sacro-spinalis the pleural reflection lies below the level of the twelfth rib, and not infrequently descends as far as the transverse process of the first lumbar vertebra.
On the right side the posterior mediastinal pleura, as it passes from the posterior aspect of the pericardium, backwards, to the front of the vertebral column, sweeps over the right side of the oesophagus; hence malignant ulcers of the oesophagus are more likely to invade the right pleura than the left. On the left side the posterior mediastinal pleura passes from the lateral aspect of the bodies of the vertebræ on to the left side of the aorta. Hence, to evacuate pus from the posterior mediastinum, there is less risk of opening the pleura if the space is entered from the left side of the vertebral column.
The seat of election for tapping the pleura (para centesis pleura) is the sixth or seventh costal interspace, a little in front of the posterior axillary fold. To allow of the introduction of a tube to drain away the pus from the pleural cavity in empyema, a portion of one of the ribs (sixth to ninth) is resected. The intercostal vessels and nerves, which lie in the groove at the inferior border of the rib, are avoided by remov ing the portion of bone subperioste ally. If the chest is opened in the scapular line, care must be taken not to resect either the seventh or the eighth ribs, which are exposed when the arm is elevated, but are overlapped by the inferior
angle of the scapula when the arm is lowered.
the bifurcation of
the trachea lies opposite, or a little below, the angulus sterni, while pos
The blue lines indicate the outlines and the fissures of the lungs. (From Cunningham.) teriorly it lies &
little below the level of the root of the spine of the scapula, opposite the fourth thoracic spine. The bifurcation takes place one vertebra higher in the infant than in the adult (Symington).
The septum between the right and the left bronchus lies a little to the left of the middle of the trachea, and the right bronchus is wider and more nearly in a line with the trachea than the left bronchus; hence the greater tendency of foreign bodies to enter the right bronchus.