184 



CIECULATION 



on the surface. The two flaplike auricles at the top of 

 the heart are separated from the ventricles by a deep 

 groove, Mhile a shallow furrow marks the division of the 

 right and left ventricles, and the position of the septum. 



On the outside may also be seen a number of large 

 blood vessels which extend from the top of the heart. In 

 addition to these there are smaller blood vessels (the coro- 

 nary system) which branch 

 over the surface of the 

 heart and supply it with 

 blood. The outside is also 

 more or less coated with fat. 

 Relation of blood vessels 

 and heart cavities. — If 

 we push bristle seekers 

 through the external blood 

 vessels, and then carefully 

 dissect away the two sides 

 of the heart we can make 

 out the course of the blood 

 through these vessels and 

 the heart. Let us first 

 examine the right side. 

 (See Fig. 68.) 



Following the course 

 of the seekers we find 

 that two large veins, 

 called the superior vena 

 cava and injerior vena 

 cava, open into the right auricle, while at the back of the 

 auricle is the opening of a small vein (the coronary vein). 

 Blood which enters the heart from these three veins passes 



_ Pig. 68 — Kight side of the heart (dis- 

 sected) ; 1, superior vena cava ; 2, infe- 

 rior vena cava : 3. right auricle ; 4, 

 tricuspid valves : 5, papillary muscle 

 fastening the threadlike chordae ten- 

 dinsB, which are, in turn, fastened to 

 the edges of Ihe valve; 6, pulmonary 

 artery, 8, aorta; 9, branches of the 

 aorta; 10, left auricle; 11, ventricle; 

 12, semilunar valves. 



