[ 6 3 ) 
and depends as much upon the fame mechanical Prim 
ciples and Structure, differing only in this, that vo- 
luntary Motion is urged by the Will, and the other 
is carried on without her Impulfe. 
XXXII. 
' - A • * ♦ 
It appears, by what we have already faid, that 
the Difpofition of mulcular Fibres to contract de- 
pends on an additional Inflation of their Cells, but 
that this cannot be done without an impelling Power 
upon the Nerve to caufe it. Now, in the Perform- 
ance of voluntary Motion, the Will muft be fup- 
pofed to make this Impulfe ; but we muft endeavour 
to find fome other impelling Caufe of Motion in 
the Mufcles of involuntary Motion to fet them to 
Work: For the mechanical Structure of all Mufcles 
is alike. 
We will produce two Examples? the Heart , and 
inteftinal Canal. 
-XXXIII... 
By a very natural Analogy between Vegetables and 
Animals, I am apt to believe, the Parts of the Ani- 
mal are perfe&ly formed in the Ovum, before its 
Egrefs from the Ovarium -, only wanting Explica- 
tion and Ex\ panfion j but that thefe two Effects can- 
not be produced, till after it has changed its place* 
and is depohted in fuch a Receptacle ais may favour 
the Propagation of thefe Effeds. Juft fo it is by the 
Seeds of Vegetables. 
This being the Cafe, in order to come at onr 
Purpofe concerning involuntary Motion, we muft 
now confider the Foetus in the Uterus , tho’ very 
j \ } v final!,, 
