EMBRYOLOGY OF THE EXTERNAL EAR

The pinna of the external ear develops from the ectoderm and mesoderm of the first and second branchial arches. Six hillocks of mesenchyme covered by ectoderm, three on either side of the first branchial cleft are visible by day 38. By day 41 these mesenchymal hillocks have fused with each other (the lobule is the last to form). The exact contribution of each hillock to the overall development of the pinna in uncertain and probably varies from individual to individual. There are probably contributions to the cartilage of the pinna and external auditory canal from the mandibular and hyoid arch mesenchyme.

The anterior and upper segments of the pinna are innervated by branches of the fifth nerve; the primordia and hillocks in this area are likely derived from the first arch. The remainder of the pinna is derived from the second arch.