[ *8i ] 
fuppofed to render thefe motions quite uncontroulable 
by the will, without Tome other etiicient caufe {h). 
Anatomy difeovers no peculiarity in the mufcular 
ftrudture of thefe parts likely to account for this ; and, 
excepting in their nerves 'having Ganglions, which 
feem indeed almoft appropriated to them, no ana- 
tomical difference has been obferved, nomechanifm, 
which thefe parts have more than thofe mufcles, which 
are fubjed to the direction of the will. 
May we not then reafonably conclude, that gang- 
lions are the inftruments, by which the motions of 
the heart and intcftines are, from the earliefr to the 
laft periods of animal life, rendered uniformly invo- 
luntary ; and that to anfwer this purpofe is their ufe, 
which they fubferve by a ftru<fture unknown to us, no 
lefs than that of the brain, though it feems not 
improbable the firft may be analogous to the laft ? 
This conclufion concerning the ufe of Ganglions 
is fupported by every truly parallel inftance. Thus 
the motions of the uvea, or mufcular circle of the 
eve ever contraaed or dilated as the eye is more or 
lefs’ irradiated with light, are as much involuntary 
as thofe of the heart j and it is known to anatomius, 
that the mufcular fibres of the uvea are fupphed by 
nerves from the lenticular Ganglion, which feems 
(h) In the beft explanation of the vital and involuntary mo- 
tions which the public has been favoured with, it is remarked by 
the moft ingenious author, « I imagine, that the mind s wane 
of power over the motion of the head is not only owing to 
its being continually afted upon by a ft.mulus, but in part to 
an original conftitution; and that, tho we fhould fuppofe this 
organ for a little while free from every degree of irritation, yet 
“ the mind, by an effort of the will, could not move it. _ Dr. 
Whytt’s Effay on the vital and involuntary motions of Animals, 
P* 3 l6, formed 
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