Involvement of Involuntary Muscle

Contraction of arrectores pilorum (smooth muscle of hair follicles) manifests as "goose bumps" (cutis anserina; Fig. 1).

• Significance

° Exposure to cold postmortem.

Seminal vesicles (smooth muscle) can contract (4).

• Significance

° Contraction leads to slight expulsion of seminal fluid at tip of penis suggesting sexual activity prior to death (Fig. 2).

Fig. 2. Semen deposition (arrowhead) on inner thigh owing to postmortem contraction of seminal vesicles.

Ciliary muscles of the iris, in rigor, alter pupil size. Pupil diameters range from 0.2 to 0.9 cm (average size = 0.4 to 0.5 cm or about 0.25 in.). The pupil outline is not always circular. Pupils can change independently and be of unequal size (Fig. 3).

• Significance

° Pupil size has no relation to the cause of death; inequality of pupil diameter does not indicate head injury.

If the myocardium of the left ventricle contracts, its wall appears thickened, and the chamber contains a small amount of blood.

• Significance

° Apparent left ventricular hypertrophy.

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