Figure 1

Morphological comparisons of mouse and human embryo development. Mouse embryonic stages (Theiler stages or TS) are based on somite number and characteristics [26]. There are 28 TS stages from the fertilization to birth, which is about 20 days post conception (dpc). Only 11 stages are shown. Human embryo stages were described by the Carnegie Institution of Washington, which are based on the developmental structures, not by size or the number of days of development [27]. The 23 Carnegie stages (CS) only covers the first 60 days of human embryo development, thereafter that the term embryo is replaced with fetus. 5 human embryos at 4-9^th week are shown here. The double headed arrows point to human and mouse embryos at similar stages of organogenesis.