8o THORAX 



its junction with the sternum. More than two-thirds of the 

 lower border are formed by the right ventricle, and the 

 remainder by the apical portion of the left ventricle, and the 

 two parts may be separated by a distinct notch. The lower 

 border is slightly concave downwards, in correspondence 

 with the upward convexity of the diaphragm on which it 

 rests, and it has a slight inclination downwards and to the 

 left. It is marked, on the surface of the body, by a line 

 extending from the sixth right costal cartilage, near the 

 sternum, to the apical point, which lies in the left fifth 

 intercostal space, or behind the left sixth costal cartilage, 

 from 80-85 mm. (3^ to 3^ inches) from the median plane. 

 The left border, which is formed mainly by the left ventricle 

 and only to a slight extent by the left atrium, extends 

 from the apex to a point on the lower border of the left 

 second costal cartilage 13 mm. (half an inch) from the margin 

 of the sternum (Figs. 33, 34, 35). 



The coronary sulcus, which indicates the plane of union 

 of the atria and ventricles and, therefore, the plane of the 

 atrio- ventricular and aortic and pulmonary orifices of the 

 heart, can be indicated, on the surface, by a line extending 

 from the sternal end of the third left costal cartilage to the 

 sternal end of the sixth right cartilage. Posterior to the left 

 extremity of that line, at the level of the upper part of the 

 third left costal cartilage, is the pulmonary orifice of the heart. 

 The aortic orifice is a little lower and slightly to the right, 

 posterior to the sternum at the level of the lower border of the 

 third left cartilage. Immediately below the aortic orifice, 

 posterior to the left margin of the sternum, at the level of the 

 upper part of the fourth left cartilage, lies the mitral orifice ; 

 and the tricuspid orifice is situated posterior to the middle of 

 the sternum, opposite the fourth intercostal spaces. The 

 positions of the great orifices cannot be confirmed at this 

 stage of the dissection, and they will be noted again, at a 

 later period, when the heart is opened. 



After the sterno-costal aspect of the heart, the boundaries 

 of the transverse sinus, and the general position of the heart 

 have been studied, the dissectors should turn the apex of the 

 heart upwards and to the right, and examine the inferior 

 and posterior surfaces whilst the heart is still in situ. They 

 will find that the inferior or diaphragmatic surface, which 

 rests upon the diaphragm, is slightly concave ; that it is 



