MAMMALIA— PHYSIOLOGY 



453 



the large aorta originates. These arteries are guarded by semi-lunar 

 valves which consist of three pouches with the convex side towards 

 the ventricle. 



Action of the Heart. — The right ventricle pumps blood through 

 the lungs, while the left ventricle forces it through the rest of the 

 body. Closely following the contraction of the auricles is the con- 



Poncreotico-_ 

 duodenal vein 



Doodenurn ■ 



Pancreas 



Post cayal vein 



Phrenic vein 



— Oo 5 fro- epiploic vein 



— Coronary vein 

 — Portal \^ein 



-Dorsal surface 

 of stomacft 



-Oosfro- splenic vein 



Anterior mesenteric vein 



Posterior mesenteric vein 



Spleen 



Fig. 246. Portal system of the cat. (Drawn by W. J. Moore, after I. M. Wilder, 



Anat. Rec, 191 9.) / 



traction of the ventricles and in this case the thick-walled left 

 ventricle contracts with more force than the right. Contraction 

 is termed systole. Relaxation is termed diastole. Besides systole 

 and diastole there is a short passive period in which there is neither 

 contraction or relaxation. 



Pulse. — In men the average frequency of the pulse is from 60 to 

 70, while in women it varies from 65 to 80 beats per minute. There 



