Human Development

During the period of morphogenesis, dramatic morphological changes take place in the embryo. In human embryology,the developmental stage of the embryo is determined based on morphological characteristics. The most commonly used staging system is the "Carnegie stage," which consists of 23 stages, ranging from stage 1 (fertilized egg) to stage 23 (8 weeks after fertilization) (O'Rahilly and Mueller, 1974). Go to Photo Gallery of Kyoto Collection