Fig. 3From: Developing an ancient epithelial appendage: FGF signalling regulates early tail denticle formation in sharksMorphogenesis of a caudal denticle. Caudal denticle placodes consist of a squamous epithelium (SE) overlying columnar cells of the basal epithelium (BE), which overlies the mesenchyme (Me) (a, d). During placode morphogenesis, condensing mesenchymal cells aggregate below columnar cells of the basal epithelium epithelial. The basal epithelium undergoes growth and folding (b, e) to form the posterior facing cusp (c, f). CB is cell layer boundary. Ameloblasts (Am) in the basal epithelial cusp (c, f) and odontodes (Od) in the papilla underlying the basal epithelium produce enameloid and dentine, respectively, to mineralise the unit [40]. Scale bars are 50 µmBack to article page