Interfollicular smooth muscle in the skin of the domesticated pig (Sus scrofa).

An interfollicular smooth muscle that spans the triad of hair follicles has been identified in the skin of the domesticated pig (Sus scrofa). This muscle has been previously noted by other investigators and identified as an arrector pili muscle. However, it cannot be interpreted as such for the following reasons: 1) It lies opposite the arrector pili muscle on the follicle; 2) the orientation of its fibers is perpendicular to those of the arrector pili; 3) the two muscles are not continuous; their attachments are different; and 4) contraction of the interfollicular muscle would have little effect on erection of the hairs. Based on structural evidence, it is postulated that upon contraction the muscle draws the base of the three aligned follicles together into a triangular conformation. In so doing, it may rotate the outer two follicles of the triad. Its specific functional role is unknown.