Human Embryo
Most embryos at stage 22 are approximately 54 postovulatory days old and measure 25-27 mm in length. Distinguishing criteria for this stage include clear formation of the external ear, the hands begin to extend ventrally beyond the body wall, the fingers of one hand may overlap the fingers of the opposite hand, thickened eyelids just begin to cover the outer margins of the eye, and the superficial vascular plexus of the head now extends about three-quarters of the way above the eye-ear level.