develops from orifice proctodeum anus MA:0000331 anal orifice WBbt:0005364 Orifice at the opposite end of an animal's digestive tract from the mouth. Its function is to expel feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as bones; food material after all the nutrients have been extracted, for example cellulose or lignin; ingested matter which would be toxic if it remained in the digestive tract; and dead or excess gut bacteria and other endosymbionts. FMA:15711 UBERON:0001245 Wikipedia:Anus GAID:312 TGMA:0001279 galen:Anus BTO:0001680 EV:0100082 TADS:0000066 proctodeum CALOHA:TS-2005 NCIT:C43362 SCTID:181262009 opening of terminal part of digestive tract anal opening digestive tract ectoderm-derived structure