1. Etiology of certain congenital structural defects
2. J. W. Ballantyne (1902 ): Manual of antenatal pathology and hygiene: the foetus . Edinburgh, p.396 .
3. J. W. Ballantyne (1904 ): Manual of antenatal pathology and hygiene: the embryo . Edinburgh, pp.76 , 76 , 76 .