Tall gut formation in the rat embryo

Summary The formation of the tail portion of the primitive gut was investigated by light and electron microscopy in 10- and 11-day rat embryos. The observations permit the conclusion that the tail gut does not form as a posterior extension of the hindgut but originates from the tail bud mesenchyme by mechanism analogous to the secondary neurulation. It includes cell condensation, aquisition of apicobasal polarity and the radial, rosette-like arrangement around a central cavity. These cells bear the cytological characteristics of both the absorptive epithelial cells and the mesenchymal cells at their apical (adluminal) and abluminal ends respectively.