Movement of palatal shelves during secondary palate closure in rat

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AbstractThe palatal shelves and tongue develop as bilateral mesenchymal elevations in the caudal portion of stomatodaeum on the medial surface of maxillary processes and the floor of stomatodaeum respectively. The shelves and tongue grow in a caudorostral direction. As the shelves are growing, their rostral ends are separated by stomatodial space from the sides of tongue and the floor of oral cavity, but their caudal portions come in close contact with the floor and the tongue. At day 15:8 the shelves are in close contact throughout their length with the tongue and the floor and there is no space in the oral cavity. The tongue grows in height and length and reaches the rostral end of nasal cavity before the beginning of shelf movement. Formation of a layer of desquamated cells between the epithelium lining the shelf and the epithelium lining the floor and the tongue precedes the separation of shelves from the floor and tongue which results in the development of space in oral cavity. The tongue which was in contact with the nasal septum and the roof of pharynx, descends and is separated from them by a uniform space. The moment the descent of tongue takes place, the shelves are ready to move to the horizontal position. Both shelves do not move at the same time, but one moves first and then the other. On assuming horizontal position both shelves fuse with each other immediately in midline during the critical period except in the most rostral region where they are separated by a gap, across which they must grow towards each other prior to fusion. Development of space in the oral cavity is an important feature during palate closure in which shelves take an active part.