. Human embryology and morphology. Embryology, Human; Morphology. 64 HUMAN EMBRYOLOGY AND MORPHOLOGY. (1) Origin of the Enamel.—The enamel is formed by the epiblast of the stomodaeum. At the sixth week the epiblast within the labial margin grows downwards so that a narrow semicircular invagination of epithelium is formed. To the plate of epiblast thus infolded the name of dental shelf is given; its position is marked superficially by an epithelial crest—the dental lower lip labio-dental groom position of oral membrane -epiblast -tongue i dental shelf (epiblast). mandib arch Fio. r enamel bud o
. Human embryology and morphology. Embryology, Human; Morphology. 64 HUMAN EMBRYOLOGY AND MORPHOLOGY. (1) Origin of the Enamel.—The enamel is formed by the epiblast of the stomodaeum. At the sixth week the epiblast within the labial margin grows downwards so that a narrow semicircular invagination of epithelium is formed. To the plate of epiblast thus infolded the name of dental shelf is given; its position is marked superficially by an epithelial crest—the dental lower lip labio-dental groom position of oral membrane -epiblast -tongue i dental shelf (epiblast). mandib arch Fio. r enamel bud of { perm, incisor _j enamel bud of 1 milk incisor r dental papilla 1 (meso-blast) :8, Section through the lip and mandible of a foetus in the third month, showing the down-growth of the Dental Shelf. ridge (Fig. 48). From its ingrowing or deep margin ten epi- thelial buds arise, both in the upper and lower jaw. Each of these twenty enamel buds or organs produces the enamel to cover the crown of a milk tooth. Each bud grows downwards and inwards from the surface and comes against a condensed formation in the mesoblast of the jaw—the dental papilla. On the papilla the enamel bud becomes partly invaginated, the papilla coming to lie within the invagination (Figs. 48 and 49). The epithelium covering the papilla becomes a layer of columnar enamel-pro- ducing cells or ameloblasts. The basal part of the ameloblasts are converted gradually into enamel, or to put it somewhat differently, they form and deposit enamel in their bases and thus produce a coating for the dental papilla. Each ameloblast is gradually converted into an enamel fibre, but their more super- ficial parts are never so converted but persists as the cuticular membrane which covers the enamel at birth and is soon after- wards worn off. The enamel of the milk teeth is completely. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration a
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
