THORACIC CAVITY 57 



face by a line, convex to the right, commencing above at the 

 lower border of the right second costal cartilage, half an inch 

 from the side of the sternum, and terminating below at the 

 sixth right cartilage half an inch from 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 incisura cordis. This 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 from 3^ 

 to 3j 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 half 

 an inch from the margin of the sternum. 



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 this line, at the level of the upper part of the 

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

 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 



