The tympanic membrane is formed by the opposition of two epithelia provided by External Auditory Canal (EAC) and the middle ear cavity, with the fibrous layer between them. Embroyologically originates from the epithelia of the EAC and the endoderm of the corresponding branchial pouch respectively. The fibrous layer originates from the branchial and mensenchyme.
Epithelium of EAC -> Ectoderm of 1st branchail cleft.
Epithelium of middle ear cavity -> endoderm of 1st branchial pouch.
Fibrous layer -> 1st branchial arch mesenchyme.
The dorsal part of the fist bronchial groove which gives rise to EAC, progressively deepens during the 2nd month. The ectoderm of the groove briefly about on the endoderm of the tub0tympanic recess ( 1st pharyngeal pouch ) , but during the 6th week , a mesodermal ingrowth breaks this contact.