THE THORAX 971 



responds with the area of precordial dtdness. Latham's circle is 

 taken as defining this area, and the directions for describing the 

 circle are as follows : ' Make a circle of 2 inches in diameter roimd 

 a point midway between the left nipple and the end of the ster- 

 mma.' Strictly speaking, the area of precordial dulness is tri- 

 angular in conformity to the V-shaped cardiac notch on the anterior 

 margin of the left limg, and it may be mapped out by the following 

 lines : one drawn from the position of the apex-beat to the median 

 line of the sternum on a level with the fourth left costcd cartilage ; 

 another drawn from the position of the apex-beat to the median 

 line of the stemvun at the junction of the body and ensiform pro- 

 cess ; and a third connecting the mesial ends of these two lines, 

 and extending along the middle of the stemvun. The inferior or 

 diaphragmatic surface, which is flat, is directed do\\Ti wards, and 

 rests upon the upper surface of the central tendon of the diaphragm, 

 covered by the serous portion of the pericardiimi. 



The outline of the heart, in reference to the anterior wall of the 

 thorax, may be indicated, with approximate accuracy, in the 

 following manner : 



Base. — Draw a line across the sternum on a level with the upper 

 border of the third right, and the lower border of the second left, 

 costal cartilages, and prolong this line for | inch to the right of the 

 sternum, and i inch to the left of it. 



Inferior (Right) Border, or Margo Acutus. — Draw a line from the 

 sternal end of the sixth right costal cartilage to the position of the 

 apex-beat. This line corresponds to the lower limit of the heart. 



Right Limit. — Draw a line from the upper border of the third 

 right costal cartUage, ^ inch from the sternum, to the sternal end 

 of the sixth right costal cartilage. This line should be curved 

 outwards to such an extent that its greatest convexity will be 

 i| inches distant from the median line of the sternum. It cor- 

 responds with the right limit of the right auricle. 



Left Border, or Margo Obtusus vel Rotundus. — Draw a line from 

 the lower border of the second left costal cartilage, i inch from 

 the sternum, to the position of the apex-beat. This line should be 

 slightly curved outwards, but it must not include the left nipple. 

 It corresponds to the left limit of the heart. 



Course of the Circulation. — The interior of the heart is divided 

 by two septa (interauricular and interventricular) into two halves, 

 right and left, and each half is subdivided by a transverse con- 

 striction into two chambers, cin upper or auricle, and a lower or 

 ventricle, right and left respectively. The auricles, except in the 

 foetus, are completely separated from each other by a septum, and 

 so also are the ventricles ; but the auricle and ventricle of each 

 side communicate freely with each other by the auriculo-ventricular 

 orifice. The right auricle receives the venous blood chiefly from 

 the superior and inferior venae cavae and the coronary sinus. 

 From the right auricle the blood passes into the right ventricle, 

 and thence into the trunk of the pulmonary artery. The right and 



