1. Asami, I., Z. Anat. Entwickl.-Gesch.139, 55–70 (1972).
2. Barclay, A. E., K. J. Franklin, M. M. L. Prichard, The foetal circulation (Oxford 1945).
3. Barcroft, J., Researches on prenatal life (Oxford 1946).
4. Born, G., Arch. mikrosk. Anat.32, 284–378 (1889).
5. Brecher, G. A., Amer. J. Physiol.176, 423–430 (1954).