THE ORGANS OF CIRCULATION 153 



IV. Find the large vessel coming up through the center of the heart. If 

 enough of it is still attached, it will be seen to curve around in back of the 

 heart. Put the wooden end of your needle tlirough it. 



A. Into what chamber does the needle penetrate? This vessel is an 

 artery known as the aorta. It sends blood by means of branches to every 

 part of the body except the lungs. 



B. Describe the walls of the aorta. 



1. Suggest a reason why arteries hold their shape instead of col- 

 lapsing. 



2. Suggest a reason why they were originally named arteries {aer 

 — air ; terin — to hold) . 



V. Locate two large vessels leading into the right aiu-icle. These are 

 two veins called the upper or superior vena cava and the lower or inferior 

 vena cava. They bring blood from all parts of the body, except the lungs, to 

 the heart. 



A. Compare the walls of these veins with the walls of the aorta. Which 

 are capable of greater movement ? Why ? 



B. What is a probable difference in function between the inferior and 

 superior vena cava ? 



C. Suggest a reason why veins do not hold their shape when empty of 

 blood. 



VI. Try to locate the pulmonary artery originating in the right ventricle 

 and the foiu* pulmonary veins leading to the left auricle. The pulmonary 

 artery takes blood from the heart to the lungs; the pulmonary veins convey 

 blood from the lungs to the heart. 



A. Suggest a reason for the blood going to the lungs. 



B. Suggest a reason for the blood retiu-ning from the lungs. 



VII. Make a simple diagram of the heart and the blood vessels connecting 

 with it. Label right auricle, left auricle, right ventricle, left ventricle, septum 

 or partition, valves, aorta, superior vena cava, inferior vena cava, pulmonary 

 artery, and pulmonary veins. 



VIII. Write a brief paragraph describing the structure of the heart. 



The organs of circulation. The arteries, veins, capillaries, and 

 heart make up the circulatory system. Approximately in the 

 center of the chest cavity, with its apex pointing toward the left, 

 is the conical-shaped heart. It is a highly muscular organ pro- 



WH. FITZ. AD. BIO. — 11 



