Corrugator cutis ani muscle

The Corrugator Cutis Ani aka Ellis' muscle, after the anatomist George Viner Ellis.

Around the anus is a thin stratum of involuntary muscle fiber, which radiates from the orifice. Medially the fibers fade off into the submucous tissue, while laterally they blend with the true skin. By its contraction it raises the skin into ridges around the margin of the anus. The name of this muscle is primarily limited to older texts.