The embryonic development of the proctodeal gland of Coturnix coturnix japonica (Aves)

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Abstract
The embryogenesis of the proctodeal gland and development of the connective tissue of the associated lamina propria in the dorsal wall of the proctodeum of Common Coturnix (Coturnix c. japonica) were studied on embryos collected at 12‐hour intervals from day 7 of incubation through hatching. Gland development began at 9.5 days from ectodermal‐derived epithelial buds developing in the craniolateral region of the dorsal proctodeal epithelium. At 11 days, the epithelial buds had become solid convoluted epithelial cords which, by 11.5 days branched to form solid individual glandular units. Lumina of the unit were formed by degeneration and vacuolization of the central cells of these solid units. Squamous epithelial caps, several layers thick, separated the vacuolizing units from the proctodeal cavity at day 13; these caps subsequently thinned, bulged into the proctodeal cavity and, by day 16, began to disappear opening the lumen of the units to the proctodeal cavity.Sequential formation of epithelial buds, by region, was: craniolateral at 9.5 days, craniomedial expansion at 10.5 days followed, beginning at 11 days, by cau‐dal expansion along entire dorsal proctodeal wall. Sequence of appearance of gland‐associated connective tissue fibers was: 9.5 days, reticular fibers already present; 11 days, collagen fibers; 11.5 days elastic fibers.Serially reconstructed models of an individual glandular unit at hatching enabled classification of the unit as a simple branched alveolar gland.