74 



ESSENTIALS OF ZOOLOGY 



or hepatic filters to eliminate urea and other waste products from the 

 blood or chemically to alter it. Pulmonary veins from the lungs 

 carry oxygenated blood. 



The venous circulation, therefore, may be divided into four main 

 systems: the systemic, hepatic portal, renal portal, and pulmonary 

 systems. 



Linqual 

 Mandibular 



Brachial. 



Sinus 



venosus 



^Internal jaqular 



External ju.julnr 



. Suipscapalar 



Innominate 



Cardiac 



Hepatic 



Cutaneous — 



Posterior 

 vena caval 





Pre cava I 



' LIVER 

 LOWER urr ;-5^0;V/,^\ 



LOBc .kV ^"^^X Hepatic 

 \ portal 



XOasfric 



Spermatic. 



Dor so. lumbar. 



Renal 



t i Splcnic 

 \_1A^_/ Mesenteric 



.SPLEEN 



Abdominal — 

 Renal portal. 

 Vesical 



External iliac 



Femoral 



Fig, 21. — Veins of the bullfrog from ventral view. (Drawn by Ruth M. Sanders.) 



The systemic veins carry the greatest load of blood to the heart. 

 The larger collecting veins of the system consist of two precavals 

 receiving blood from the anterior parts of the body, except the lungs, 

 and a single postcaval or posterior vena cava receiving blood from 

 the posterior parts of the body. The two precavals empty into the 

 anterior end of the sinus venosus of the heart, and the posterior vena 

 cava empties into its posterior end. 



