ANATOMY OF THE HEART AND BLOOD-VESSELS 291 



FIG. 102. Diagram representing a sec- 



produces a sound which can be recognized through the stethoscope. 

 In later stages great quantities of liquid may accumulate in the 

 pericardium so as seriously to impede the heart's beat. 



The Cavities of the Heart. On opening the heart (see diagram 

 Fig. 102) it is found to be subdivided by a longitudinal partition 

 or septum into completely separated right and left halves, the 

 partition running from about 

 the middle of the base to a point 

 a little on the right of the apex. 

 Each of the chambers on the 

 sides of the septum is again in- 

 completely divided transversely, 

 into a thinner basal portion into 

 which veins open, known as 

 the auricle, and a thicker ap- 

 ical portion from which arteries 

 arise, called the ventricle. The 

 heart thus consists of a right 



auricle and ventricle and a left ti ugh the Heart fr m base * apex " 

 auricle and ventricle, each auricle communicating by an auric- 

 uloventricular orifice with the ventricle on its own side, and 

 there is no direct communication whatever through the septum 

 between the opposite sides of the heart. To get from one side to 

 the other the blood must leave the heart and pass through a set 

 of capillaries, as may readily be seen by tracing the course of the 

 vessels in Fig. 100. 



The Heart as seen from its Exterior. When the heart is viewed 

 from the side turned towards the sternum (Fig. 103) the two 

 auricles, Aid and As, are seen to be separated by a deep groove 

 from the ventricles, Vd and Vs. A more shallow furrow runs 

 between the ventricles and indicates the position of the internal 

 longitudinal septum. On the dorsal aspect of the heart (Fig. 104) 

 similar furrows may be noted, and on one or other of the two fig- 

 ures the great vessels opening into the cavities of the heart may be 

 seen. The pulmonary artery, P, arises from the right ventricle, 

 and very soon divides into the right and left pulmonary arteries, 

 Pd and Ps, which break up into smaller branches and enter the 

 corresponding lungs. Opening into the right auricle are two 

 great veins (see also Fig. 102), cs and ci, known respectively as 



