1. R. Getty, 1975 : Sisson and Grossman's, The Anatomy of domestic Animals , Vol. 1 , 5th ed ., pp. 278 -279 and278 ; Vol. 1 , pp. 278 and278 -279 . Philadelphia-London-Toronto. W. B. Saunders Company.
2. R. Nickel, A. Schummer, and E. Seiferle, 1968 : Lehrbuch der Anatomie der Haustiere , Vol. I , 3rd ed ., pp. 61 -67 , Berlin and Hamburg, Paul Parey.
3. T. Koch, 1976 : Lehrbuch der Veterinar-Anatomie , Vol. I , 3rd Ed ., p.97 . Jena, VEB Gustav Fischer Verlag.