A Human Embryo of Streeter Age Group XIII

Abstract

A human embryo was serially sectioned and was reconstructed with 172 sections. The length of the embryo was estimated to be 5.6 mm. The embryo was characterized by optic evagination with thickened lens ectoderm, absence of lens pits, the otic vesicle without endolymphatic appendage, distinct arm buds and leg buds, lung buds and absence of the ureteric buds. All these above mentioned findings corresponded to those expected in Streeter age group XIII. Although age group XIII and XIV share some features seen in this embryo, absence of lens pits was most helpful to distinguish this embryo from Streeter age group XlV. This embryo did not show any notable developmental abnormalities. Thus we concluded that this embryo was normally developed and was in the age group XIII of Streeter's developmental horizon.