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.

http://upload.wikimedia.org/wikipedia/commons/7/75/Anorectum.gif, http://upload.wikimedia.org/wikipedia/commons/6/65/Protovsdeuterostomes.svg

anal opening, anal orifice, opening of terminal part of digestive tract

uberon

proctodeum

anal

UBERON:0001245

http://purl.obolibrary.org/obo/uberon.owl, http://purl.obolibrary.org/obo/cl.owl

In the lungfish, sharks and rays the rectum opens into the cloaca which also receives wastes (urine) from the kidneys and material from the reproductive organs. In bony fish the rectum reaches the outside environment through the anus, which is normally situated just in front the urinary and reproductive openings. However in some fish the digestive tract may be curled back on itself, and in the Electric Eel (Electrophorus electricus) the anus is situated in the fish's throat. -- http://www.earthlife.net/fish/digestion.html

• terminal part of digestive tract