Embryonic Development of the Olfaci'ory Organ in Mice

The development of the olfactory organ in the prenatal stages of mice (Patch/normal Balb/c) was studied. Eight stages were selected for this study; they are 9, 10, 11, 12, 13, 14, 16 and 18 days of gestation. At 9 days of gestation, the olfactory placodes begin to appear as two thickenings of epidermis, latero-ventral to the prosencephalon. At 10 days, the primary choanae appear; each lies between the lateral and medial nasal swellings. At 11 days, the epithelia of these swellings fuse (closing the primary choanae) to form the nasal fin. This fin is mostly regressed and becomes replaced by mesenchymal cells except in its most posterior part to forffi the bucconasal membrane. As development proceeds and at 12 days, the secondary choanae are formed. At 11 days, the epithelium of the middle septal region evaginates to form the vomeronasal organ which is kidney-shaped. At 16 days and thereafter, this organ becomes seperated from its cartilagenous envelope by a thick layer of cavernous tissue and the vomeronasal glands appear. At 12 days, the lateral nasal epithelium evanigates into the lateral nasal wall to form the middle meatus. In addition, and at 14