Mesenchyme in the middle ear.
D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D002781:Cholesteatoma / Q000196:embryology; D004432:Ear, Middle / Q000166:cytology / Q000196:embryology*; D006801:Humans; D051381:Rats; D013997:Time Factors; D014432:Tympanic Membrane / Q000166:cytology / Q000196:embryology