1. Bedford, D. E., Papp, C., and Parkinson, J. (1941). Brit. Heart J., 3, 37.
2. Gould, S. E. (1953). Pathology of the Heart. Thomas, Springfield, U.S.A. Hamilton, W. S., Boyd, J. D., and Mossman, H. W. (1952). Human Embryology. Heffer and Sons, Cambridge.
3. Hudson, R. (1954). Brit. Heart J., 16, 472.
4. Human Embryology and Morphology;Keith, A.,1948