A Human Embryo of Streeter Age Group XX

Abstract

A human embryo was obtained from a total hysterectomy specimen of a 31-year old woman. This embryo was serially sectioned and studied with special reference to its developmental stage. The developmental characteristics of the eight key organs in this embryo corresponded well to the age group XX. The embryo was 23 mm in crown-rump length, and was 55 days old on the basis of the last menstrual period. The digestive tract was well-developed, and the dorsal and ventral pancreases were thought to be fused with each other. The development of the respiratory system was in normal commencement, having branched more than three times. The mesonephroi and metanephroi were also well-developed and the lumen of the ureter was visible. The heart was composed of four chambers and almost all of the valves present in the normal adult heart were also noted. The telencephalon was relatively small, and the ventricles of the brain were narrow.