Mr . Home's Lecture 
214 
a portion of the external intercostal muscles from the chest of 
a dog/ and in that way saw very distinctly the two sets of 
muscles in action. The fibres of both sets contracted exactly 
at the same time. 
The particular structures of these different forms of muscles, 
and the mechanical advantages arising out of them, have been 
already explained in former lectures upon this subject ; but 
there is a form of muscle, in which the disposition of fibres pro- 
duces a considerable saving of muscular^ contraction, that has 
not been at all taken notice of. 
The muscle I allude to is the heart, the most important 
in the body, whether we consider the frequency of action, 
or the office in which that action is employed ; and we shall 
find, upon examination, that the fibres are disposed differently 
from those of any other muscle, which disposition of fibres ap- 
pears to have a superiority, in being enabled to produce their 
effect by a smaller quantity of contraction. 
In considering the muscular structure of the heart, it is only 
intended to examine that part of it called the ventricles, which 
may be reckoned two separate muscles. The right ventricle, 
for sending the blood through the vessels of the lungs, called 
the lesser circulation ; the left, to propel it through the 
branches of the aorta, which go to every part of the body, 
called the greater circulation. 
If these two ventricles are superficially examined, the mus- 
cular partition by which they are united seems to belong equally 
to both, one half of it appearing to be a portion of the right, 
the other of the left ventricle. 
In this view, the sides of the left ventricle, although evi- 
dently more muscular and thicker than those of the right, are 
