130 



GENERAL ZOOLOGY 



gill capillaries are thus intercalated in the arterial system. In 

 the frog a similar condition exists in the tadpole, but with the 



development of the lungs and 

 other changes accompanying 

 metamorphosis, the gills are 

 resorbed, and the branchial 

 arteries become the three pairs 

 of arterial arches of the adult 

 frog (Fig. 81). 



Blood is returned to the sinus 

 venosus of the frog's heart 

 through three large venous 

 trunks, viz., a right and left 

 precava or anterior cava, and a 

 single postcava. The anterior 

 cavae drain blood from the 

 capillaries of the head and the 

 anterior part of the body. 

 The postcava has its roots in 

 the segmental renal veins which 

 collect blood from the kidneys. 

 The principal venous trunks of 

 each hindleg are the sciatic and 

 femoral veins. At the juncture 

 of the leg with the body each 

 femoral vein bifurcates to form 

 a pelvic vein and an external iliac 

 vein. The two pelvic veins 

 unite in the mid-line to form 

 the anterior abdominal vein 

 which proceeds forward in the 

 mid-line of the abdominal wall 

 to join one of the branches of 

 the hepatic portal vein. The 

 external iliac vein unites with 

 the sciatic to form a renal portal 

 vein, which terminates in capil- 

 laries in a kidney. Each kidney receives oxygenated blood from 

 segmental renal arteries, given off by the dorsal aorta, and it also 

 receives venous blood from the renal portal vein. The blood is 



Fig. 81. — Diagram of the circulatory 

 system of the frog from the ventral side. 

 a, anterior abdominal vein; a. a., aortic 

 arch; c.a., common carotid artery; Co., 

 coeliac artery; d.a. ; dorsal aorta; f, femo- 

 ral vein; il, iliac artery; k, kidney; l, 

 liver; lu, lung; p, pancreas; p. a., pulmo- 

 nary arch; p.c, postcava; p.e., pelvic 

 vein; pk, precaval vein; p.v., pulmonary 

 vein; r.a., renal artery; r.p., renal portal 

 vein; r.v., renal vein; a, sinus venosus; 

 sc, sciatic vein; st, stomach. 



