MICHAEL ALLABY. "rectum." A Dictionary of Zoology. 1999. Encyclopedia.com. 21 Dec. 2009 <http://www.encyclopedia.com>.
MICHAEL ALLABY. "rectum." A Dictionary of Zoology. 1999. Encyclopedia.com. (December 21, 2009). http://www.encyclopedia.com/doc/1O8-rectum.html
MICHAEL ALLABY. "rectum." A Dictionary of Zoology. 1999. Retrieved December 21, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O8-rectum.html