AMPHIBIA 



281 



veins, which carry the blood from these parts back to the heart, 

 the capillaries, which are very small vessels connecting the arteries 

 and veins. (Figure 151.) 



Structure of the Heart. — The heart of the frog, situated in the 

 anterior part of the body cavity ventral to the liver, lies within a sac, 

 the pericardium, whose cavity is completely cut off from the coelom. 



£x ternol jugular 

 Infernal juqulor 



Left auricle 



Hepafic vein 



Coslric t^e/'n 

 HepoliC porfol vein 

 Duodena/ vein — 



Jnfesfinol vein - 



Sp/enic vein - 



Ren of vein ^^ 



Renol porfol vein 



Vesical vein , 



Sciotic '/ein — 



Righf auric fe 



-Pre-cavat 



Sinus venosus 



^ — Pulmonary 

 Cardiac yein^^^^CfSrochiof vein 



—Lunq 



-Musculofenous 



■L iver 



Abdominal vein 

 ■PostccivaJ veir) 

 ■Testis 

 Spermafic vein 



- -J /Sidney 



OorjO'/mnbar vein 



— Abdominal vein 



Pelvic vein 



femoral vein 



Fig. 151. Venous system of the frog. Dorsal view. (After Parker and Haswell. 



Courtesy of Macmillan and Co., Ltd.) 



although originally continuous with it in early development. In 

 Amphibians and in Reptiles, the heart has three cavities, two auricles 

 and one ventricle. 



The venous blood from the body is received into the right auricle 

 and the purified blood from the lungs into the lejt. Both throw 

 their contents into the ventricle which pumps the mixed blood in 

 two directions, partly to the lungs and partly around the system. 



