CIRCULATOEY SYSTEM 323 



The auricles lie at the base of the heart, on its 

 dorsal aspect, the auricular appendices being the only 

 parts of them visible on the ventral surface. 



a. The right ventricle forms the right side of the 



ventricular portion, but does not reach to the 

 apex. It is soft to the touch. 



b. The left ventricle forms the left side and apex of 



the heart ; and is firmer than the right ventricle, 

 owing to the greater thickness of its walls. 



c. The left auricle is anterior to the left ventricle, 



and is largely concealed by the great vessels. It 

 is produced ventrally into the ear-like auricular 

 appendix. 



d. The right auricle is dorsal to the base of the 



right ventricle, and is produced in front into the 

 auricular appendix. 



The roots of the great vessels, 

 a. Opening into the right auricle. 



i. The right anterior vena cava returns blood from 

 the right side of the head, neck, and thorax, 

 and from the right fore-limb. It enters the 

 thorax at its anterior end, and runs back 

 along the inner side of the right lung, to open 

 into the right auricle by an aperture in its 

 dorsal wall. 



ii. The left anterior vena cava returns blood from 

 the left side of the head, neck, and thorax, 

 and from the left fore-Hmb. It runs back 

 along the inner side of the left lung, and 

 crosses between the heart and the root of the 

 left lung, to open into the left side of the right 

 auricle. 



iii. The posterior vena cava returns blood from all 

 parts of the body behind the diaphragm. It 

 enters the thorax through an aperture in the 



T 2 



