Anus
the opening at the lower or posthe lower or posthrough which the through which the excrement or waste ANZAC products of digestion are expelled. With regard to its anatomy, it is sufficient to state that it is kept firmly closed on ordinary occasions by the external and internal sphincter muscles, the former of which contracts the integument around the opening, and, by its attachment to the coccyx behind, and to a tendinous center in front, helps the levator ani muscle in supporting the aperture during the expulsive efforts that are made in the passage of the fæces or intestinal evacuations; while the latter, or internal cular muscular fibers of the lowest part sphincter, is an aggregation of the cirof the rectum, and acts in contracting the extremity of the tube. The integument around the anus lies in radiating plaits, which allow of its stretching without pain during the passage of the fæces; and the margin is provided with a number of sebaceous glands.