-
3
Week 3
IE: Auditory placode; auditory pit
ME: Tubotympanic recess begins to develop -
4
Week 4
IE: Auditory vesicle (otocyst); vestibular-cochlear division
EE: Tissue thickenings begin to form -
5
Week 5
EE: External auditory meatus begins -
6
Week 6
IE: Utricle and saccule present; semicircular canals begin
EE: Six hillocks evident; cartilage begins to form -
7
Week 7
IE: One cochlear coil present; sensory cells in utricle and saccule
EE: Auricles move dorsolaterally -
8
Week 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 -
9
Week 9
ME: Three tissue layers at tympanic membrane are present -
11
Week 11
IE: Two and one-half cochlear coils present; nerve VIII attaches to cochlear duct -
12
Week 12
IE: Sensory cells in cochlea; membranous labyrinth complete; otic capsule begins to ossify -
15
Week 15
ME: Cartilaginous stapes formed -
16
Week 16
ME: Ossification of malleus and incus begins -
18
Week 18
ME: Stapes begins to ossify -
20
Week 20
IE: Maturation of inner ear; inner ear adult size
EE: Auricle is adult shape but continues to grow until age 9 -
21
Week 21
ME: Meatal plug disintegrates, exposing tympanic membrane -
30
Week 30
ME: Pneumatization of tympanum
EE: External auditory canal continues to mature until age 7 -
32
Week 32
ME: Malleus and incus complete ossification -
34
Week 34
ME: Mastoid air cells develop -
35
Week 35
ME: Antrum is pneumatized -
37
Week 37
ME: Epitympanum is pneumatized; stapes continues to develop until adulthood; tympanic membrane changes relative position during first two years of life