limb buds from 4- and 4.5-week-old human embryos were cultured on agar medium consisting of medium 199 , chick embryo extract and horse serum for 4 days with or without thalidomide ( 1-1.5 microgram/ml ) , and the direct effect of thalidomide was examined morphologically in histological preparations .
C0282505
limb buds
C0868971
human embryos