64 LABORATORY DIRECTIONS 



In the auricles locate the pulmonary veins and venae cavae. 

 Near the opening of the inferior vena cava is the entrance of the 

 coronary sinus. The inter auricular septum possesses a thin area, 

 th.t fossa ovalis, which may be felt by running a finger over the 

 septum. In fetal life there is an opening, the foramen ovale^ 

 between the two auricles. 



The wall of the right ventricle is distinctly thinner than that 

 of the left. The columns of muscle on the inner surfaces are 

 known as traheculae. The opening between right ventricle and 

 right auricle is guarded by the tricuspid valve, so named because 

 it consists of three membranous flaps, one dorsal, one ventral, 

 and one on the inter-ventricular septum. The valve between the 

 left auricle and left ventricle is the bicuspid or mitral valve. 

 Numerous strands of connective tissue, the chordae tendineae 

 join the flaps of the valves to the walls of the ventricles or to 

 papillary muscles (muscular projections of the walls). The 

 aorta leaves the left ventricle on the right side; the pulmonary 

 artery leaves the right ventricle on the left side. The entrances 

 to both aorta and pulmonary artery are guarded by semilunar 

 valves. 



Study the structure and action of all of the valves of the 

 heart. Understand how they operate and at what phases of 

 the heart beat each valve is open and closed. If necessary, con- 

 sult physiology textbooks. 



