90 ANALYTIC SECT. X. 
SECTION X. 
Arterial Irritability. 
cov. It has been a favourite notion with 
many eminent physiologists, to lay the whole 
stress of the circulation on the heart, and to regard 
the arteries as inert tubes; but they are so imme- 
diately connected with all the important operations 
of surgery, and have been so frequently brought 
under consideration, that their real functions are 
now pretty well understood. The animal economy 
is a vast assemblage of organs, where each per- 
forms its peculiar office, and yet concurs with the 
rest in one grand design. ‘The operation of one 
organ cannot, therefore, be magnified at the ex- 
pense of another, without a jar in some part of 
the system. 
ccvu. All the arteries are derived from the 
aorta, and are in fact only divisions and sub- 
divisions of it. The coats of the aorta are strong 
and dense in the vicinity of the heart, but where 
it divides into branches, they become thin and 
