Tanaka, Tadashi, and Hans K. Uhthoff. “The Pathogenesis of Congenital Vertebral Malformations: A Study Based on Observations Made in 11 Human Embryos and Fetuses”. Acta Orthopaedica, vol. 52, no. 4, Jan. 1981, pp. 413-25, doi:10.3109/17453678109050122.