Embryology of the Ear

Week 3

3

IE: Auditory placode; auditory pit
ME: Tubotympanic recess begins to develop

Week 4

4

IE: Auditory vesicle (otocyst); vestibular-cochlear division
EE: Tissue thickenings begin to form

Week 5

5

EE: External auditory meatus begins

Week 6

6

IE: Utricle and saccule present; semicircular canals begin
EE: Six hillocks evident; cartilage begins to form

Week 7

7

IE: One cochlear coil present; sensory cells in utricle and saccule
EE: Auricles move dorsolaterally

Week 8

8

IE: Ductus reuniens present; sensory cells in semicircular canals
ME: Incus and malleus present in cartilage; lower half of tympanic cavity formed
EE: Outer cartilaginous third of external canal formed

Week 9

9

ME: Three tissue layers at tympanic membrane are present

Week 11

11

IE: Two and one-half cochlear coils present; nerve VIII attaches to cochlear duct

Week 12

12

IE: Sensory cells in cochlea; membranous labyrinth complete; otic capsule begins to ossify

Week 15

15

ME: Cartilaginous stapes formed

Week 16

16

ME: Ossification of malleus and incus begins

Week 18

18

ME: Stapes begins to ossify

Week 20

20

IE: Maturation of inner ear; inner ear adult size
EE: Auricle is adult shape but continues to grow until age 9

Week 21

21

ME: Meatal plug disintegrates, exposing tympanic membrane

Week 30

30

ME: Pneumatization of tympanum
EE: External auditory canal continues to mature until age 7

Week 32

32

ME: Malleus and incus complete ossification

Week 34

34

ME: Mastoid air cells develop

Week 35

35

ME: Antrum is pneumatized

Week 37

37

ME: Epitympanum is pneumatized; stapes continues to develop until adulthood; tympanic membrane changes relative position during first two years of life