Embryology of the Ear 

Inner Ear : Separate 

Middle & External Ear : from the 1st and 2nd Branchial Arches 

Inner Ear 

• Thickening of surface Ectoderm (Otic Placode) on each side of caudal part of hindbrain 

• It invaginates and sinks deep into the underlying mesenchyme to form (Otic Pit)

• Edges of otic pit comes together to form (Otic Vesicle or Otocyst) which is considered as (Primordium of membranous labyrinth)

• Otic vesicle loses its connection with surface ectoderm.

• A diverticulum grows from the otic vesicle and elongates to form Endolymphatic duct and sac (1st to develop)

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• Otocyst is differentiated into 2 parts:

1. Dorsal Utriclar part: ==> Endolymphatic duct, utricle & semicircular ducts

2. Ventral Saccular part: ==> Saccule & cochlear duct

From the ventral saccular part:

• Tubular diverticulum grows (Cochlear duct) and coils to form the membranous cochlea

• Saccule connected with cochlea by Ductus reuniens (narrowest segment)

• Organ of corti (Spiral organ) differentiate from cells in the wall of cochlear duct

• Ganglion cells of the 8th nerve migrate along the coils of membranous cochlea and form spiral ganglion

• Nerve processes extend from this ganglion to the spiral organ and terminate on the hair cells

• Periotic Duct: within the cochlear aquaduct, connects the scala tympani to the posterior cranial fossa​

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 From the Dorsal utricular part:

• 3 disclike diverticula grows out from the utricular part, the central parts of these diverticula fuse and disappear (Semicircular Ducts)

• Attached to the utricle, later enclosed in semicircular canals of bony labyrinth (from mesenchyme around otic vesicle)

• At one end of each semicircular duct a dilatation Ampullae, inside it differentiate the specialized receptors area (cristae ampullares)

•   In the utricle and saccule (maculae)

Middle Ear 

- Tubotympanic Recess from the Endoderm of 1st Pharyngeal POUCH.

1. Proximal part form Eustachian tube

2. Distal part become Tympanic cavity (which envelop the ossicles, their tendons, ligament and corda typani)

• -  Late fetal period, expansion of tympanic cavity gives rise to mastoid antrum (in the petromastoid part of the temporal bone)

• -  Middle ear reaches Adult SHAPE at Birth.

• -  No Mastoid air cells present at Birth.

• -  Mastoid develops from the Squamous and Petrous bones.

• -  Petrosquamosal suture may persist as a bony plate (Korner’s septum) separating superficial squamosal cells from the deep petrosal cells.

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• -  By 2-3 years of age the mastoid cells are well developed and produce conical projections of the temporal bone (mastoid process)

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1. First Branchial Arch (Meckel’s cartilage):

• -  Malleus Head and neck (Mesoderm)

• -  Anterior Malleal ligament,

• -  Incus Body and Short process (Mesoderm)

2. Second Branchial Arch (Reichert’s cartilage):

• -  Handle of the Malleus

• -  Long process and Lenticular process of the incus

• -  Stapes (except vestibular part of footplate and Annular ligament from Otic capsule)

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•  Upper parts of ossicles derived from 1st ARCH

•  Lower parts of ossicles derived from 2nd ARCH