English: Somites are formed in the PSM through interactions between the somitogenesis clock and other factors. These oscillations form prospective somite boundaries, which eventually form somites. The oscillations frequency is 4 times higher in snakes than in mice, resulting in the production of more but smaller sized somites in the snake. This acceleration of the somitogenesis clock is presumably responsible for most of the increase in the snake’s vertebral number. Picture and Caption Information sourced from below publication ^[1]