28 UNIVERSITY OF MISSOURI STUDIES 



lower part of the sixth left sternochondral articulation. 

 The left border extends upward, with a marked outward 

 curve, from the apex point to the middle of the second 

 left costal cartilage. Its greatest distance from the mid- 

 line is about 9 cm. in the fourth intercostal space. 



The outline as here mapped out is formed by all four 

 chambers of the heart. The right auricle which is some- 

 what distended, forms the right half of the base, the entire 

 right border and a small portion of the inferior border. 

 The right ventricle forms the remainder of the inferior bor- 

 der, with the exception of a small strip near the apex which 

 is formed by the left ventricle. It also forms the left half 

 of the base and the upper portion of the left border, where 

 the conus arteriosus rises above the left auricle. The left 

 ventricle forms the small part of the inferior border about 

 the apex and the lower two-thirds of the left border. The 

 left auricle forms the short strip between the left ventricle 

 and the conus arteriosus (Plate XXXII). 



When viewed from the left side (Plates XXXI and 

 XXXV) the main part of the heart is formed by the -left 

 ventricle with the left auricle above and behind it. The 

 right ventricle forms the anterior boundary of the heart 

 and separates the left ventricle from the sternum. The up- 

 per half of the posterior boundary is formed by the left 

 auricle while the lower half is formed by the right auricle, 

 with a small part of the left ventricle near the apex (Plates 

 XI and XII). 



When viewed from the right side (Plates XXX and 

 XXXIV) the larger part is formed by the right auricle, 

 with the right ventricle and its conus arteriosus forming 

 the anterior boundary and the left auricle forming the up- 

 per half of the posterior boundary. 



The positions of the orifices are indicated in Plates 



