A Human Embryo of Streeter Age Group XV

Abstract

A human embryo was sectioned serially and studied microscopically in order to determine its proper age group based on the developmental status of the internal organs in terms of selected definable characteristics. The embryo obtained incidentally from an hysterectomy specimen had an ovulation age of 33 days and a crown-rump length of 7.4 mm. Discernible morphological features of the embryo included closure of the lens vesicle, separation of the otocyst from skin ectoderm and endolymphatic duct, a cervical sinus, a narrow atrio-ventricular canal with an incompletely formed interventicular septum, bronchi in the primary stage, and dorsal and ventral pancreatic buds. The above observations strongly suggested that this embryo should be classed in the age group XV of Streeter's developmental horizon.