[The early development of the Jacobson's organ in the cat (Felis silvestris)]

The histological study of the nose of an embryo of the cat (Felis silvestris 10 mm) presents a simple cavity which caudally communicates with the oral cavity by a narrow cleft, the primitive choana. This aperture results from the former rupture of the membrana bucconasalis of which the present material still contains remnants. Compared to the simple nasal cavity, the organ of Jacobson, situated at the base of the broad fetal nasal septum, shows a progressive development. From this one might conclude, according to ontogenetical rules, an early functional importance of the accessory olfactory organ. The currently fetal nose under investigation presents the organ as a primary open groove which increases in depth from rostral to caudal. Only caudally, a short section of the organ is already formed into a tube. From the functional point of view, the epithelial lining of this organ is still undifferentiated, but its dorsal part is clearly thickened. It seems that this indicates an early arrangement of the later olfactory epithelium. Beside this it is striking that in early fetal life, the organ of Jacobson extends to a remarkable length within the nasal cavity. Obviously the organ occupies, early in ontogeny, its area inside the little developed nose. Finally, the striking resemblance of the topography of the organ of Jacobson between early embryos of mammals and those of fetal and even some adult reptiles is discussed.