SUGGESTIONS FOR LABORATORY WORK 613 



like the finger of a glove. At varying distances from the base it 

 is attached to the heart and vessels. Trim the pericardium along 

 or near the line of attachment. 



General Topography of the Heart. The apex is conical, smooth, 

 firm, and fleshy, and is formed by the muscular ventricles. Notice 

 that the left ventricle is larger and has thicker walls than the right 

 ventricle. The base is irregular and wider. It presents not only 

 the thin-walled auricles but also vessels and fat. 



The Vessels. The aorta and pulmonary artery maintain a cylin- 

 drical form and their cut ends are naturally circular. The great 

 veins have thinner walls in proportion to their size and collapse 

 more or less completely. The inferior vena cava forms nearly a 

 right angle with the long axis of the heart. The superior vena cava 

 is at the base on the ventral surface. The pulmonary artery is the 

 prominent vessel on the ventral aspect between the two auricles, 

 extending from the base of the right ventricle. The aorta, with 

 its principal branch, will be seen more distinctly at a later stage. 



Dissection of the Heart. The order of dissection follows the 

 course of the blood through the organ. Bear in mind that, al- 

 though anatomically united and acting together as muscles, as 

 to their cavities, the right and left sides of the heart are entirely 

 separated by complete partitions between the two auricles and 

 between the two ventricles. When the cavities are open wash 

 their interiors with running water. The flowing water will show 

 how the valves close the openings between the cavities and also 

 the action of both sets of semilunar valves. 



Opening the Right Auricle. Hold the heart with its ventral side 

 toward you. Push the point of the scissors into the upper and outer 

 angle of the appendix and cut toward the median line of the heart. 

 Lift the edge of the flap and note the wide mouths of the great 

 veins. The right, the superior; the left, the inferior vena cava. 

 In the back wall of the auricle at the base of the inferior vena cava 

 will be found an oval scar, the fossa ovalis. Near the orifice of the 

 inferior vena cava is a ridge, the eustachian valve. 



Opening the Right Ventricle. This must be done very carefully. 

 At a point on the ventricle at a short distance from the pulmonary 

 artery, insert the point of a scalpel and cut parallel with the fur- 

 row, extending to the apex of the right ventricle. Keep the cut 

 edges of ventricular walls apart while studying the cavity. 



