Figure 1.

Frontal sections through a 54-day fetus displaying a degrading seam in the hard palate and a multilayered medial edge epithelial seam in the soft palate. (A,A′) The posterior boundary of the hard palate is distinguished by the medial processes of the palatine bones. A fragmenting medial edge epithelial seam is present (arrowhead). (B,B′) The middle soft palate is identified by the presence of the aponeurosis and absence of palatine bone. A medial epithelial seam appears to be present but is hard to distinguish with H & E staining (arrowhead). (C,C′) The coverslip was removed on an adjacent slide to (B) and stained with pan-cytokeratin antibody. The antibody distinguishes epithelium (arrowhead) from mesenchyme. All epidermal and endodermal (posterior tongue, oropharynx) epithelia are stained with the antibody. (D,D′) The posterior soft palate has a very thick medial seam that is stained weakly with pan-cytokeratin antibody (arrowhead). Ap, aponeurosis; ns, nasal septum; pb, palatine bone; t, tongue. Scale bars: (A) 1 mm, (A′) 200 μm and applies to B′ and D′, (C′,E′) 100 μm.