Rectum 

hemroids a varicose dilatation of a vein of the superior or inferior hemroidsal plexus, resulting from a persistent increase in venous pressure.

Hemroids: (A), internal; (B), external; (C), combined; (D), thrombosed.

external h. a varicose dilatation of a vein of the inferior hemroidsal plexus, situated distal to the pectinate line and covered with modified anal skin. 

internal h. a varicose dilatation of a vein of the superior hemroidsal plexus, originating above the pectinate line, and covered by mucous membrane. 

mixed h. a varicose dilatation of a vein connecting the superior and inferior hemroidsal plexuses, forming an external and an internal hemroids in continuity. 

prolapsed h. an internal hemroids which has descended below the pectinate line and protruded outside the anal sphincter. 

strangulated h. an internal hemroids which has been prolapsed sufficiently and for long enough time for its blood supply to become occluded by the constricting action of the anal sphincter. 

thrombosed h. one containing clotted blood.