1. Spencer R: Conjoined twins; Embryology, pathogenesis, and review of the literature. (monograph in preparation)
2. Conjoined twins: Theoretical embryologic basis;Spencer;Teratology,1992
3. Development stages in human embryos;O'Rahilly;Carnegie Institution of Washington, Publication,1987
4. Exstrophia splanchnica. (Exstrophy of the cloaca.);Spencer;Surgery,1965