Blockage of the Inferior Hæmorrhoidal Nerve for Operation on Hæmorrhoids

I. Anatomy TWo sphincters guard the anal canal, the external sphincter and the internal sphincter. The external sphincter.?The external .sphincter is composed of the subcutaneous part, the superficial part, and the profundus or the deep part. The subcutaneous part is composed of muscle fibres surrounding the anal orifice, and is intimately connected with the skin. It is supplied by perineal branches of the fourth sacral nerve. The superficial part is composed of muscle fibres which rise from the coccyx, sweep round the anus and are inserted in the perineal body. Some fibres curve round the anterior margin of the anus to form a sling. It is supplied by the inferior hsemorrhoidal and the fourth sacral nerves. The profundus part is a true sphincter muscle. It is composed of non-striped muscle fibres. It has no bony attachment. It is in intimate contact with the pubo-rectalis portion of the levator ani. It is supplied by the inferior hsemorrhoidal nerve. The internal sphincter.?The internal sphincter is a thickening of the circular non-striped muscle fibres of the gut, and is continuous with the circular muscle-coat of the rectum. It surrounds the upper two-thirds of the anal canal. It is supplied by the second and third sacral