THE VERTEBRATE BODY 



343 



through the liver, where poisons and foreign bodies are removed ; and 



so on. 



A trip through the circulatory system of man would be somewhat 

 similar. We would notice that the erythrocytes are considerably smaller, 

 they are disc-shaped rather than elliptical, and they do not have a nucleus 

 as the frog red blood cells have. The thrombocytes are disc-shaped 

 rather than spindle-shaped. We would not have passed through the 



Infernal jugular 



External jugular 

 Subclavian V. 

 Innominate V. 

 Superior vena cava 

 Pulmonary V. 



Heart 



Inferior vena cava 



- Hepatic portal 

 Renal V. 



-Common ilia V. 



Fig. 23.11. The larger veins of the human body. All of the veins carry unoxygenated 

 blood except the pulmonary veins which bring the freshly oxygenated blood from the 



lungs to the heart. 



kidney on our way to the heart, for only arteries take blood to the kid- 

 neys in man. Neither would we have gone through a sinus venosus, for 

 this structure is not present in the higher vertebrates. Also, man has 

 four chambers rather than three in his heart, so we would not have en- 

 tered the same ventricle twice. Because of this extra ventricle there is 

 no chance for the oxygenated and unoxygenated blood to mix, for there 

 is a separate auricle and ventricle for each type of blood. 



We should not close our discussion of the circulatory system without 

 mentioning lymph, since this substance is such an important aid in the 



