| Abstract: | In the course of this investigation 24 fetuses of the Sprague-Dawley rats were used. Pregnant animals were sacrificed at 12, 14, 16, 18, and 20 days of gestation. The fetuses were removed and fixed in buffered formalin solution. The heads were dehydrated, embedded in paraffin, and the nasal cavities were sectioned serially. Light microscope observations were made on 10 to 15 μ thick sections stained with H and E, Mallory's trichrome stain, and Gomori's alkaline phosphatase stain. The 12 day old fetus possessed well developed olfactory depression with a thick epithelial covering. The olfactory fossa was still separated from the buccal cavity by a solid layer of young mesenchyme. In the 14 day old fetus the communication between the nasal and buccal cavities was established. The palatal shelves developed still vertically. All the turbinates and the nasal capsule were already differentiated. The glandular system was represented with the main and two to three accessory excretory ducts. During the sixteenth day of prenatal development, the sinus and the sinus related glands became for the first time evident. The ossification of the membranous parts of the lateral nasal wall was initiated. In the next two developing stages the maturation of the cartilage, the increasing ossification in the membrane, and the further differentiation of the glands were the major morphological changes in the formation of the lateral nasal wall. |
