THE HEAET AND GKEAT VESSELS. 1405 



intercostal space and the superior border of the third costal cartilage. The 

 left auricle lies behind the second left intercostal space, close to the edge of the 

 sternum. 



The diaphragmatic or inferior surface of the heart rests upon the diaphragmatic 

 or basal part of the pericardium. The lase, or true posterior surface, of the heart is 

 formed mainly by the left atrium, which is moulded posteriorly upon the oesophagus, 

 the aorta, the bronchi, and the bronchial glands, the pericardium intervening. 

 The left atrium extends behind the right atrium for a considerable distance to the 

 right of the median plane. 



In a radiographic examination in cases of general visceroptosis, the diaphragm, 

 which should rise and fall opposite the xiphisternal junction, will be seen to be an 

 inch or more lower down, while the heart is seen to hang more vertically than 

 normal (cardioptosis). 



In determining the position of the cardiac orifices and their valves it is to be 

 remembered that they are all situated below and to the left of the anterior part 

 of the coronary sulcus, and that they lie in the following order from above down- 

 wards yi z>j pulmonary, aortic, mitral, and tricuspid. When delineated on the 

 surface they will be seen to lie within an ellipse whose long axis extends from the 

 superior 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 superior border of the third left chondro-sternal junction ; the aortic 

 orifice, directed upwards, backwards, and to the right, lies further from the surface, 

 behind the left half of the sternum, opposite the inferior border of the third costal 

 cartilage ; the mitral orifice lies at an inferior 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, lies very obliquely behind the right half of the sternum at the 

 level of the fourth and fifth cartilages and intervening space. 



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 cavity 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 inferior 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 

 laterally, and will therefore escape injury if the puncture is made at a safe distance lateral to 

 the internal mammary vessels, viz. , one inch lateral to the left border of the sternum. 



To establish free drainage in suppurative pericarditis, the sixth left costal cartilage must be 

 resected and the internal mammary vessels ligatured ; the transversus thoracis and the pleural 

 reflection are then pushed aside and the pericardium exposed and incised. 



The ascending aorta lies behind the sternum, opposite the second and third ribs, 

 and, unless dilated, does not project beyond its right border. The superior 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 superior border of the manubrium. 



The innominate and left common carotid arteries diverge from either side of the 

 median 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 medial 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 lies behind the superior part of the manubrium sterni, 

 the right behind the medial end of the right clavicle. The superior vena cava lies 

 immediately 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 

 atrium, behind the third chondro-sternal articulation, corresponds to the centre of 

 the root of the right lung. 



