1. Kent, G.C.: Comparative Anatomy of the Vertebrates, New York : Blackiston Co., 1954, p 88.
2. Lockley, R.M.: The Private Life of the Rabbit, London: A. Deutsch Ltd., 1964, p 145.
3. Parker, T.J., and Haswell, W.A.: A Textbook of Zoology, vol II, London: MacMillan, 1962, p 774.
4. Romer, A.S.: Man and the Vertebrates, 3rd ed, Chicago: University of Chicago Press, 1943, p 166.
5. Thompson, H.V., and Worden, A.N.: The Rabbit, London: Collins , 1956, p 7.