IX.] 



THE COMMON FROG. 



129 



This process of blood oxygenation is termed respi- 

 ration, and the organs which subserve it are termed 

 respiratory or breathing organs. Such organs in 

 man are the lungs. The central organ of circulation 

 in man is, as all know, the heart, which is a muscular 

 organ, divided into four chambers, or cavities. 



\XS. 



Ao. / 



II. 



RX 



Fig. 76.— I. The left side ; an 1 II. the right side' of the Heart of Man dissected. 

 \.—LA, the left auricle; PV, the four pulnmnary veins; cd, a style passed 

 through the aiiriculo-ventri ular aperture; MW, the mitral valve; nb. a style 

 passed through the left ventricle into the aorta ; J?A, RV, parts of the right side 

 of the heart : Pa, pulmonary artery. 

 II. — RA, the right auricle; VCS, superior vena cava; VCI, inferior vena cava, 

 the styles, y^, cd, being passed through them into the auricle ; ab, style parsed 

 through the aurlculo-ventricular aperture ; Tl^, tricuspid valve ; RV, right ven- 

 tricle : SL, semi-lunar valves at the base of PA, the pu'monarv artery, through 

 which the style ^/i is passed ; LA, LV, auricle and ventricle of the left side of 

 the heart. 



These chambers are called "auricles" and "ven- 

 tricles," and there are two of each — there being an 

 auricle and a ventricle on the right side and also on 

 the left. 



Blood that has performed its nutritive functions, 

 and is therefore charged with carbonic acid gas, is 



K 



