CIECULATORY SYSTEM. 439 



The heart is conical, with the apex directed backwards and 

 slightly to the left side. A line of fat, which encircles it, 

 marks externally the division into auricular and ventricular 

 portions. 



1. The auricular portion is anterior in position, and forms 



the base of the cone. It is thin-walled, dark in 

 colour, and divided into right and left auricles, the 

 division being indicated externally by a Une of fat. 



2. The ventricular portion is posterior, and forms the apex 



of the cone. It is much thicker-walled than the 

 auricular portion, and paler in colour. The division 

 between right and left ventricles is not obvious 

 externally. 



B. The Veins. 



The veins should be dissected before the arteries, as they 

 lie for the most part nearer the surface. Great care must be 

 taken not to cut or tear them, as bleeding occurs freely , and is 

 apt to be very troublesome. If a complete dissection is re- 

 quired, the venous system should be injected from either the 

 femoral or the jugular vein. 



1. Veins openings into the right auricle. The right auricle 

 receives the venous blood from the whole of the body 

 by three large veins, the vense cavse. 



a. The right anterior vena cava returns blood from 

 the right side of the head and neck, the right 

 wing, and the right side of the breast. 



It is a short wide vein, about a quarter of an 

 inch in length, opening into the right anterior 

 angle of the right auricle : it is formed by the 

 union of three principal veins. 



i. The right jugular vein runs along the right side 

 of the neck, close to the vertebral column, and 

 dorsal to the oesophagus. 



Anteriorly it unites with the left jugular 

 vein, on the under surface of the base of the 



