[The early development of Jacobson's organ in the nasal cavity of the rat before the inception of the secondary palatal development].
The early development of Jacobson's organ was studied by means of a series of embryos of the rat which were of various ages and exactly dated. Already at the youngest stage of those rats, the nasal cavity is just an open groove, the organ is a thickened epithelial layer at the medial nasal process. Only 15 h later, while the nasal grooves start to close from caudal to rostral, Jacobson's organ has acquired the shape of a deep, long cleft, situated within the broad nasal opening. On the 13th d of fetal life, a complete, caudally closed nasal cavity appears. By the means of fundamental growth changes, the already well developed organ has become shifted to a more caudal position and lies now above the primary palate. A shorter caudal part of the still cleft-like organ just starts to close itself thus forming its typical tube-like structure. Moreover strong nerve bundles running from Jacobson's organ to the brain indicate that in the meantime a sensory epithelium can be distinguished. Up to the 15th d of development, the tube-forming process of Jacobson's organ is completed. Parallel to this procedure, the surrounding nasal cavity acquires a caudal apertura nasalis interna by the rupture of the membrana bucconasalis while Jacobson's organ still lies above the rostral primary palate. Primary in the medial, somewhat later in the lateral part of the nasal cavity, first outlines of cartilage appear, visible as dense cell formations. Together with this, the paraseptal cartilage, in these stages closely connected to the septal cartilage, develops quite early. Between the 14th and 15th d of its fetal life, the flat, tube-formed Jacobson's organ of the rat gets turned from a primary horizontal into a vertical position, which brings its sensory epithelium to the medial side. It is assumed that this happens for functional reasons. Because of the obviously early and progressive development of Jacobson's organ within that of the nasal cavity, it seems to be probable that already the origin of the nose, the olfactory placodes, are determined in the directions both of the nasal cavity and of Jacobson's organ. Furthermore the results demonstrate an early preferential development of Jacobson's organ in comparison to that of the surrounding nasal cavity.
Wöhrmann-Repenning
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Institut für Zoologie und vergleichende Anatomie, Universität Kassel.
D000818:Animals; D009296:Nasal Cavity / Q000196:embryology*; D010159:Palate / Q000196:embryology; D051381:Rats / Q000196:embryology*; D012679:Sense Organs / Q000196:embryology*
Zur frühen Entwicklung des Jacobsonschen Organs in der Nasenhöhle der Ratte vor Beginn der sekundären Gaumenbildung.