PALATAL SHELF ELEVATION IN WISTAR RAT FETUS

Author:
  • MFM W Ferguson
    M W Ferguson
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  • 1 January 1978
    • journal article
    • research article
Abstract
Palatogenesis in the Wistar rat fetus was studied macroscopically and microscopically between days 13-19. A statistical analytical method was devised whereby the developmental ages of the fetuses were calculated from the smear ages of the litters adjusted for individual variations in crown-rump lengths. Palatal shelf elevation occurred in vivo between days 16.3-16.5. Experimentally induced shelf elevation in freshly delivered fetuses was sluggish at day 14 but by day 16.3 occurred in less than 1 s. The matrix of the shelf mesenchyme (especially anteriorly where shelf elevation began) showed an increasing accumulation of mucopolysaccharides from days 14-16.3 and became increasingly edematous. Prior to elevation the palatal shelf was progressively undercut by epithelial invagination which provided a fulcrum for this event. The extreme posterior part of each shelf (future soft palate) was horizontal from the beginning. Only the anterior 1/5 of each shelf fused with the nasal septum; behind this a common nasal passage was formed. The space needed to create (simultaneous with shelf elevation) the common nasal passage was made available by flattening of the tongue and protrusion of its tip out of the oral cavity, such protrusion being facilitated by the sloping bulge of the primary palate and nasal septum. Many existing theories of shelf elevation were inconsistent with the observations. Shelf elevation occurred very rapidly at a rather precise developmental stage and turgor, due to binding of water to mucopolysaccharides, was the source of a rising intrinsic shelf elevating force, a force which at day 16.4 reaches a threshold level enabling the shelves to force their way up and over the intervening tongue.

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