External features of the 18-mm embryo.
Keywords: arm, auricle (pharyngeal arch 1), auricle (pharyngeal arch 2), buttock, cerebral vesicle prominence, cervical fold, digit 1 (great toe), digit 1 (thumb), external acoustic meatus (branchial groove 1), external nostril, foot, forearm, frontonasal elevation, hand, heart prominence, lateral nasal elevation, leg, lens, liver prominence, lower eyelid fold, mammary gland primordium, mandibular prominence of pharyngeal arch 1, maxillary prominence of pharyngeal arch 1, maxillonasal groove, medial nasal elevation, neck region, primitive rima oris, rim of optic cup, thigh, umbilical cord, upper eyelid fold
Source: Atlas of Human Embryos.