1. Thompson, J. S. & Thompson, M. W. Genetics in Medicine 4th edn (W. B. Saunders, Philadelphia, 1986).
2. Moore, K. L. The Developing Human 3rd edn (W. B. Saunders, Philadelphia, 1982).
3. Leek, I. Br. Med. Bull. 40, 390–395 (1984).
4. Witkop, C. J., MacCollum, D. W. & Rubin, A. in Handbook of Congenital Malformations (ed. Rubin, A.) 103–156 (W. B. Saunders, Philadelphia, 1967).
5. Burdi, A. R. & Silvey, R. G. Cleft Palate J. 6, 1–7 (1969).