£ 45 ] 
Momentum of the Fluids to enter again into the con- 
tracted Mufcles, willinftancly dilate and diftrad them,, 
when the Isnpulfe of the Will ceafes, till an exad 
Equilibration is reftored. 
. XCVIL 
This being the plain Matter of Fact in regard to 
the voluntary Mufcles; let us now endeavour to 
find out the Mechanifm belonging to the involun- 
tary ones, and more particularly of that very curi- 
ous one the Heart. 
XCVIIL 
Dr. Hoadly , in his Lectures on Refpiration y hag 
manifeftly fhewn that* the external Ranges of the in- 
tercoftal Mufcles appear to have all the charaderiftic 
Marks of antagonist Mufcles. If you take three Ribs 
together, fays he, and obferve the different Ranges 
of the Fibres in the two intercoflal Mufcles, which 
lie on each Side the middlemoft of thefe Ribs; yon 
will fee, at firCt Sight, that the internal Range in the 
lower Mufclc, counter acts directly the external 
Range in the upper Mufcle. 
XC1X. 
The Action of the diaphragm is alfo counter- 
balanc'd by the abdominal Mufcles, and Contents of 
the Abdomen 5 which fqueeze it up, in a convex 
Form, into the Cavity of the Thorax 7 upon every 
Expiration. 
As 
