1. Anosa, V. O. &Isoun, T. T. (1975).Bulletin of Animal Health and Production in Africa,23, 337–340.
2. Bain, R. V. S. (1957).Ceylon Veterinary Journal,5, 2–7.
3. Bain, R. V. S. (1959).British Veterinary Journal,115, 365–369.
4. Bancroft, J. D. &Stevens, A. (1982).Theory and Practice of Histological Techniques. 2nd edn. Churchill Livingstone, Edinburgh. pp. 278–296.
5. Blood, D. C., Radostits, O. M. & Henderson, J. A. (1983).Veterinary Medicine. 6th edn. Ballière-Tindall. p 591.