140 HANDBOOK OF ANATOMY 



The muscles are of three kinds : 



Columns Carneas bundles of muscle-fibre raised in relief on> 

 the walls of the ventricle. 



Papillary Muscles which are attached at each end to the- 

 walls of the ventricles, but are free in the middle. These pre- 

 vent over-distension. 



Chordae Tendinese thin bundles of muscle-fibre from the 

 bases of the papillary muscles to the apices of the cusps of 

 the valves. 



The Valves of the Heart and large vessels are circular 

 orifices with semilunar flaps of muscle (cusps) projecting inwards 

 from the circumference. These meet in the middle and com- 

 pletely close the orifice. A rush of blood pushes these forward, 

 and the cusps automatically close the orifice when the flow 

 ceases. This keeps the blood flowing in one direction and 

 prevents regurgitation. 



The Pericardium is a fibro-serous sac surrounding the heart. 

 It is attached to the diaphragm all round the inferior surface 

 of the heart, and is prolonged upwards, being gradually lost 

 on the great vessels. The inferior vena cava pierces the peri- 

 cardium posteriorly. 



The Arteries. 



The arteries are the bloodvessels which leave the heart and 

 break up into capillaries for the supply of the tissues. There 

 are two systems of circulation the pulmonary, consisting 

 of the pulmonary artery leaving the right ventricle and 

 ending in the pulmonary veins which enter the left auricle;, 

 and the systemic, consisting of the aorta leaving the left ven- 

 tricle and ending in the superior and inferior venae cavae which 

 enter the right auricle. 



The Pulmonary artery arises from the base of the right 

 ventricle of the heart. It is a short vessel about 2 inches long. 

 It passes upwards to the left of the ascending aorta, and termi- 

 nates by dividing into right and left pulmonary arteries, which 

 enter the roots of the right and left lungs respectively. 



The Aorta rises from the base of the left ventricle of 

 the heart. It passes upwards, backwards, and to the left,. 



