444 DISSECTION OF THE PIGEON. 



right side of the heart therefore contains venous blood, and 

 the left side arterial blood. 



Open the pericardial cavity so as to expose the heart fully ; 

 and dissect away the connective tissue and fat from the vessels 

 at the base of the heart. 



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 ven- 

 tricular 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 line 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 opening into the right auricle. The right auricle 

 receives the venous blood from the whole of the 

 body by three large veins, the vense cavae. 



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. 



