rx.] THE COMMON FROG. 135 



blood is checked on the right side {if), while on the 

 left it runs freely into the pulmo-cutaneous trunks 

 (r and /), and thus the respiratory structures receive 

 unmixed venous blood for purification. 





Fig. 79. — Diagram of section of Frog's Heart. LA, left auricle ; RA, right auricle ; 

 V, ventricle ; s, moveable septum dividing the left aortic passage Ip from the right 

 aortic passage ip w, valve ; 3, 3, aortic trunks leading to/, pulmonary artery, and 

 r, cutaneous respiratory artery; 2, 2, aortic trunks going to form the great dorsal 

 aorta ; cgld, carotid gland interrupting the flow of blood into /, the lingual artery, 

 and c, the carotid artery. 



As the lungs get gorged with blood, the resistance 

 on the two sides of the septum of the bulb becomes 

 at first equalised and soon becomes the greater on the 

 left side ; then the septum is forced over to the left, 

 and the blood, now mixed with pure blood, flo^ving in 

 from the left auricle, flows freely along the systematic 

 arteries (2 and 2). The obstruction of the carotid 

 glands {c gld) being the greatest and the last to be 

 overcome, the carotid and lingual arteries [c and /) 

 receive the very last of the blood — that, namely, 

 which coming from the left auricle is purely arterial — 



