1. Howe, Herbert M., Mossman, Harlan, andOpitz, John: Personal communications.
2. Developmental horizons in human embryos;Streeter,1951
3. Human embryology;Hamilton,1962
4. Timing of human congenital malformations;Millen;Develop. Med. & Child. Neurol.,1963
5. The borderland of embryology and pathology;Willis,1958