involuntary muscle n.
Any of the smooth muscles, except for the cardiac muscle, not under control of the will.
An involuntary muscle, following the half-ordained bidding of the brain, had moved perhaps three inches toward her breast.
What few minutes I have now I owe to having trained what most folk call an involuntary muscle.
Microscopically the spleen has a fibro-elastic coat in which involuntary muscle is found (fig. 2).
The heart is the only involuntary muscle in which contractions can be excited by these experiments.