CIRCULATION.] PHYSIOLOGY. 57 



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vena cava ; /. V.C. inferior vena cava : P;A- pulmonary artery ; Ao^ aorta; 

 A'o\ innominate branch from aorta dividing into subclavian and carotid , 

 arteries ; L. lung ; Tr. trachea, i, solid cord often present, the remnant of '^ 

 a once open communication between the pulmonary artery and aorta. 2, 1 

 masses of fat at the bases of the ventricle hiding from view the greater 

 part of the auricles. 3, line of fat markintj the division between the two < 

 ventricles. 4, mass of fat covering the trachea. 



I 



is represented in Fig. 5. If you could look through 1 

 the front of your own chest, and see your own heart \ 

 and lungs in place, you would see something not so )^ 

 very very different. ^ 



If now you handle the heart — and if you want to 

 learn physiology you must handle things — you will have 

 no great difficulty in finding the great yellowish tubes ' 

 marked Ao and A'o' in the figure. Your butcher 

 perhaps may not have cut them across exactly where 

 mine has done, but that will not prevent your recogni- ! 

 zing them. You will notice what thick stout walls they 1 

 have, and how they gape where they are cut. Ao 

 is the aorta, and A'd is a great branch of the aorta, 

 going to the head and neck of one side, perhaps the 

 branch along which we imagined just now that you, a 

 poor little red blood-corpuscle, were travelling. If you 

 were to put a wire through A'd you would be able to 

 bring it out through Ao, or vice versct. But what is 

 P. A. which looks so much like the aorta, though you 

 will find that it has no connection with it 1 You 

 cannot pass a wire from the aorta into it. It also is 

 an artery, the pulmonary' artery. We shall have 

 more to say about it directly. 



Now try and find what are marked in the figure 

 as S. V. C. and /. V. C. You will perhaps have a little 

 difficulty in this; and when you have found them 

 you will understand why. They are the great veins ,. 



;-'>-i 



* From j^ulmo, Ivais : the artery of the lung. 



