MICHAEL ALLABY. "yak." A Dictionary of Zoology. 1999. Encyclopedia.com. 6 Jul. 2009 <http://www.encyclopedia.com>.
MICHAEL ALLABY. "yak." A Dictionary of Zoology. 1999. Encyclopedia.com. (July 6, 2009). http://www.encyclopedia.com/doc/1O8-yak.html
MICHAEL ALLABY. "yak." A Dictionary of Zoology. 1999. Retrieved July 06, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O8-yak.html