62 ANATOMY OF THE RAT 



to send blood throughout the body than through the pul- 

 monary circulation. Observe the trabeculae carneae on the 

 inner surface of the left ventricle's wall. The aortic ori- 

 fice, surrounded by the aortic valve, is the opening into the 

 aorta. Part of the valve may have been torn in opening 

 the ventricle. The mitral, or bicuspid valve surrounds 

 the mitral orifice, through which blood passes from the 

 left atrium to the left ventricle. Note the chordae tendi- 

 neae extending from this valve also to the ventricular wall. 

 The ventricular septum is the muscular partition between 

 the cavities of the right and left ventricles. Open the left 

 atrium, wash out the coagulated blood, and find the orifices 

 of the pulmonary veins. How many openings are there? 

 View the partition between the atria (the atrial septum) 

 by strong transmitted light. The fossa ovalis is the trans- 

 lucent area which will be seen in this septum. Ask the 

 instructor to explain its significance. 



Exercise XVI. Make a diagrammatic sketch of the internal 

 anatomy of the heart. 



The arteries and veins posterior to the heart will be 

 studied after the examination of the respiratory, digestive, 

 and urinogenital systems. 



