part of part of existence ends during embryo stage oral epithelium nasal cavity epithelium nasal fin The nasal fin is an epithelial seam that develops by fusion between the epithelial linings of the medial and lateral nasal swellings. Shortly after its formation the nasal fin regresses and is replaced by mesenchyme, with exception of its most posterior portion which remains as the bucconasal membrane. UBERON:0009671 FMA:295940 EHDAA2:0004548