on Muscular Motion. 217 
cavity they are blended with the fibres of £he opposite por- 
tion. 
That portion which is opposite to the septum is composed, of 
three sets of fibres ; those of the external set are nearly longi- 
tudinal ; the two others, which lie under it, decussate each other, 
and are obliquely transverse in their direction, one passing a 
little upwards, the other downwards ; and both terminate upon 
the edge of the septum. 
In the structure of this muscle we find none of the mecha- 
nical advantages, so obvious in the left ventricle ; the want of 
these, however, is in some measure compensated by its situa- 
tion ; for the blood contained in its cavity, will have the vis 
inertia overcome, and a direction given to its course by the 
action of the apex of the left ventricle : that motion only re- 
quiring to be continued, and accelerated, for which purpose the 
structure of this muscle is very well calculated ; and in which 
it will also be assisted by the lateral swell of the septum into 
its cavity, in the contraction of the left ventricle. v 
In the course of this lecture, it has been my endeavour to 
show the most simple structure that is capable of muscular ac- 
tion ; and to point out the advantages intended to be produced 
by the different complications which occur in an animal 
body. 
The view which I have taken of this subject gives us an 
idea of the extent to which muscular action is employed in 
different animals ; and leads to the belief, that very dissimilar 
structures in the more perfect animals are endowed with this 
principle, since the actions of the smaller arteries, as well as of 
the absorbent vessels, must be referred to it. 
Ff 
MDCCXCV. 
