During the 20th century, the human vomeronasal organ (VNO) has been controversial regarding its
structure, function, and even identity. Despite reports that provide evidence for its presence throughout
prenatal and postnatal ontogeny, some studies and numerous textbooks declare its absence in late fetal and
postnatal humans. To that end, the present study was designed to establish firmly whether the human VNO
is homologous with that of other mammals and whether it degenerates (partially or completely) or persists
throughout prenatal development. Fifty human embryos and fetuses (33 d to 32 wk fertilisation age) and 2
neonates were examined by light microscopy. Four embryonic primates (mouse lemurs) were examined for a
comparison of VNO embryogenesis. The presence or absence and structural characteristics of the VNO and
supporting tissues are described. The first appearance of the VNO was in the form of bilateral epithelial
thickenings of the nasal septum, the vomeronasal primordium. The primordia invaginated between 37 and
43 d of age and formed the tubular VNO. The tubular VNO was located dorsally at a variable distance
from, but was always spatially separated from the paraseptal cartilages. The mouse lemurs examined in this
study and other reports from the literature indicate that the human VNO resembles that of primates having
functional VNOs until just after a tubular VNO is formed. Examination of the VNO and adjacent tissues
suggested that the VNO may lose receptor cells and corresponding vomeronasal nerves and become a
ciliated, pseudostratified epithelium between ∼ 12 and 14 wk of age. Our findings indicate the prenatal
human VNO goes through 3 successive stages: early morphogenesis, transformation (of the epithelium), and
growth. These observations indicated that (1) all embryonic humans develop a vomeronasal organ which is
homologous with the VNOs of other mammals, but which has become displaced and highly variable in
relative location during embryogenesis; (2) the human vomeronasal organ does not degenerate prenatally,
but very likely loses the functional components of the vomeronasal complex of other mammals; and (3) the
remnant of the human VNO persists until birth and beyond.