1 56 CIRCULATORY SYSTEM. 



apex of which would be next to the heart. The same rule 

 holds in regard to the venous system, it being observed, how- 

 ever, that the latter has two trunks connected with the heart in- 

 stead of one. The general rule is, therefore, established through- 

 out the vascular system, that the collective area of the branches 

 is always greater than that of the trunk from which they pro- 

 ceed.* By the same rule the circulation in the branches must 







^* I am indebted to a scientific friend, Mr. Erskine Hazard, for the following 

 computation, by actual measurement, of the arteries, from which it appears that 

 in many of them, at least, the area of the trunks is greater than that of the 

 branches near them. 



The Left Carotid at the Aorta is .42 



Its diameter at the branching is 43 



Increase of diameter - 01 



Its square at the Aorta is ........ 1764 



Each Carotid branch measures .28, and the sum of their squares 



is 1568 



The difference of the areas of the Carotid and its branches is 12 per cent, in 

 favour of the Carotid. 



Diameter of Aorta near the Iliacs - .64 



Its square - - . ' - 4096 



Diameter of Left Iliac - 40 



Its square 1600 



Diameter of Right Iliac 37 



Its square 1369 



Sum of their squares 2969 



Aorta largest by nearly 38 per cent., or - 1127 



Square of Right Iliac, as above, 1369 



Ditto External Iliac 900 



Ditto Internal do. 729 



1629 



Branches largest by nearly 19 per cent., or 260 



