THE FROG — A REPRESENTATIVE VERTEBRATE 



409 



the flow in the internal carotid. It contains a spongy network which re- 

 sists blood flow and becomes somewhat distended when the heart con- 

 tracts. When the heart is relaxed, it contracts and aids the flow. 



Each aortic arch curves dorsally and posteriorly, giving off an artery 

 to the back (the occipitovertebral) and one to the arms (the subclavian). 

 The left and right arches then unite to form a median dorsal aorta that 

 continues posteriorly, ventral to the vertebral column. The aorta sup- 

 plies the abdominal viscera (except for the lungs), trunk and hind legs 

 (Fig. 21.12). Among the structures supplied is the spleen, an organ in 

 which blood cells are produced, stored and destroyed. 



The pulmocutaneous arch carries blood to organs where gas ex- 

 change with the external environment occurs. Each vessel soon divides 

 into a pulmonary artery to the lungs and a cutaneous artery. The latter 

 supplies not only the skin, but also much of the lining of the mouth 

 and pharynx. 



Veins. The veins returning blood to the heart have a more com- 

 plex pattern. The digestive tract and associated organs are drained by 



Carotid arcK" 



xternal ca-rolid artery 

 •Internsd carolid artery 



Aortic arcH 



PulmocutaileoS s^ch. 



Anterior 

 vena Cava' 



Subclavian. ' 

 vein.' 



Brachial vein" 



Hcpati 



Musculocutarjeous vein 



Dorsal aorta 



Coeliacoinese-r!t«,ric artery 



Dorsolumbar vein 



Posterior vena cava' 



Ren 2*1 artery and vein. 



Renal portal vein 



Ventral abdominalvcin 



Pelvic vein 



Femoral artery 

 and vein 



Occipito-.-ertebral aortziy 



PrjUmanaxy artery & vein 



Subcla-vian arttry 



Cutaneous 



arterjr 



Hepatic portal . 

 •^ •" vein 



Hepatic artery 



Gastric artery 

 and vein 



Mesenteric arteiy i vein 

 Splenic cirtery & vein 

 >^x\v// Iliac artery 



^Posterior mesenteric 



ajrtery 



Sciatic artery 

 and vein. 



Figure 21.12. A ventral view of the major arteries and veins of the frog. Veins are 

 shown in black;* arteries are white. Certain of the anterior veins have been omitted 

 from the right side of the drawing and certain of the anterior arteries from the left side. 



