D2 SURFACE AND SURGICAL ANATOMY. 
The left auricle extends behind the right auricle for a considerable distance to the 
right of the mesial plane. 
In determining the position of the cardiac orifices and their valves it is to be 
remembered that they are all situated to the left of the right auriculo-ventricular 
groove, and that they lie in the following order from above downwards—viz. pul- 
monary, aortic, mitral, and tricuspid. When delineated on the surface they will 
be seen to lie within an ellipse whose long axis extends from the upper border of 
the third left to the sixth right chondro-sternal junction. 
The pulmonary orifice, directed upwards and slightly backwards and to the left, 
lies opposite the upper part of the third left chondro-sternal junction; the aortic 
orifice, directed upwards, backwards, and to the right, hes further from the surface, 
behind the left half of the sternum, opposite the lower border of the third costal 
cartilage ; the mitral orifice lies at a lower level behind the left half of the sternum, 
opposite the fourth rib; the orifice of the opening is directed downwards, forwards, 
and to the left. The tricuspid orifice, situated nearer the anterior wall of the chest 
than the mitral, hes opposite the middle of the sternum at the level of the fourth 
and fifth cartilages and intervening space; the orifice, which is placed very 
obliquely, may be represented upon the surface. by an ellipse placed parallel to and 
immediately to the left of the middle two-fourths of the line indicating the anterior 
part of the right auriculo-ventricular groove. 
Although the first and second sounds of the heart are heard all over the cardiac area, the 
sounds produced by the individual valves are heard most distinctly, not directly over their ana- 
tomical situation, but over the area where the cav ity in which the valve lies approaches nearest 
to the surface. Hence the mitral sound is best heard over the apex (mitral area), the tricuspid 
over the lower part of the body of the sternum (tricuspid area), the aortic over the second right 
costal cartilage (aortic area), and the pulmonary over the second left intercostal space (pulmonary 
area). 
In tapping the pericardium (paracentesis pericardii) the pleura will be avoided by making the 
puncture through the fifth or sixth left intercostal space as close as possible to the edge of the 
sternum. When, however, the pericardial sac is distended with fluid, the pleura is pushed out- 
wards, and will therefore escape injury if the puncture be made at a safe distance external to the 
internal mammary vessels, viz. 1 in. external to the left border of the sternum. 
To establish free drainage j in suppurative pericarditis, the sixth left costal cartilage must be 
resected and the internal mammary vessels ligatured ; the triangularis sterni and the pleural 
reflexion are then pushed aside and the peric avdium exposed and incised. 
The ascending aorta lies behind the sternum, opposite the second and third ribs 
and, unless dilated, does not project beyond its yight border. The upper border of 
the aortic arch lies at or a little above the centre of the manubrium sterni; in the 
child the vessel may reach as high as the upper border of the manubrium. 
The innominate and left common carotid arteries diverge from either side of the 
mesial plane between the upper part of the manubrium sterni and the front of the 
trachea. A pin pushed directly backwards immediately above the middle of the 
supra-sternal notch will strike the inner border of the innominate artery a little 
below its bifurcation. 
The pulmonary artery lies behind the left border of the sternum opposite the 
second interspace and the second costal cartilage. 
The left innominate vein hes behind the upper part of the manubrium stern, 
the right behind the inner end of the right clavicle. The superior vena cava les 
behind and a little to the right of the margin of the sternum, opposite the first 
and second interspaces and the intervening second rib; its opening into the right 
auricle, behind the third chondro-sternal articulation, correspi mds to the centre of 
the root of the right lung. 
(sophagus. —The av erage leneth of the cesophagus in the adult is 10 in. 
25 cm.); the distance from the incisor teeth to its commencement is 6 in.; to the 
point or level where it is crossed by the left bronchus, 9 in.; to the cesophageal 
opening of the diaphragm, 14 to 15 in.; to the cardiac orifice of the stomach, 16 in. 
These measurements, which are of great importance in diagnosing the seat of 
cesophageal obstructions, should be marked off from below upwards upon all 
cesophageal bougies and probangs. Posteriorly, the c@sophagus extends from the 
level of the sixth cervical spine to that of the ninth dorsal, a little to the left of 
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