Chap, x.] THE THORAX. 159 



sternum. The vessel proceeds upwards under cover 

 of the second left cartilage. The aortic orifice is behind 

 the left border of the sternum close to the lower edge 

 of the third cartilage. The trunk ascends behind the 

 second cartilage of the right side, and would be 

 wounded by a stab through that cartilage close to 

 the sternum. The concavity of the aortic arch corre- 

 sponds to the point between the first and second pieces 

 of the sternum. The auriculo-ventrieular orifices are 

 behind the sternum, the right being opposite the fourth 

 spaces, and the left on a level with the fourth carti- 

 lages. The innominate and left carotid arteries come 

 off at a spot corresponding to the middle of the maim- 

 brium, and run behind the right and left sterno-cla- 

 vicular joints respectively. The superior vena cava 

 would be wounded by a knife entering either the first 

 or the second right interspace close to the sternum. 

 The left innominate vein lies transversely just below 

 the upper border of that bone. The right auricle 

 would be wounded in stabs passing through the sternal 

 ends of the third, fourth, and fifth cartilages on the 

 right side, or through the corresponding intercostal 

 spaces if the knife be kept fairly near to the sternum. 

 (See Fig. 16, which shows the relations of the heart 

 and great vessels as given by Riidinger, and which 

 differ somewhat from the above account.) 



A circle with a diameter of two inches, and 

 with its centre midway between the nipple and the 

 end of the gladiolus, would approximately define 

 that part of the heart which lies immediately behind 

 the chest wall,, and is uncovered by lung or pleura 

 (Latham). 



Wounds of the heart most frequently involve the 



right ventricle, that segment of the heart being the 



' part most exposed anteriorly. Next in frequency is 



the left ventricle wounded, and then the right auricle. 



Other things being equal, a wound of the ventricle is 



