Maternal hypoxia in early pregnancy can result in malformations of the vertebrae of mouse foetuses, and there is a tendency for more posterior vertebrae to be affected the later in pregnancy the oxygen deprivation occurs (Murakami & Kameyama, 1963). Ingalls et al. (1957) and Degenhardt (1954, 1959) had earlier obtained similar results.
We have also exposed pregnant mice to X-radiation and studied the consequent malformations. The effects on the extremities have already been described (Murakami, Kameyama & Nogami, 1963), and in the present paper we shall describe the effects on the vertebral column. Vertebral malformations in animals irradiated in utero have been described by Job, Leibold & Fitzmaurice (1935), Warkany and Schraffenberger (1947), Russell. (1950, 1954), and Russell & Russell (1954).
In order to obtain results comparable with those of our experiments with hypoxia, no less than to detect inter-strain differences, we used mice of the ddN and CF1 strains originally supplied by the Central Laboratories for Experimental Animals, Tokyo (Zikkendobutsu Chuo Kenkyujo).