1. BACHMAN, C. (1927). Amer. J. Obstet. Gynec., 14, 797.
2. Manual of Ante-natal Pathology and Hygiene"-"The Foetus;BALLANTYNE, J.W.,1902
3. Ibid., "The Embryo";BALLANTYNE, J.W.;Klin. Mbl. Augenheilk,1904
4. COFFEY, V. P., and CLARKE, N. (1960). J. Irish med. Ass., 46, 139.
5. CRAIG, W. (1886). Edinb. med. J., 32, 193.