The document provides an overview of the embryonic development of the ear, detailing the formation of the external, middle, and inner ear structures. It covers the differentiation of components such as the cochlea, semicircular canals, and the tympanic cavity, as well as the role of sensory cells in hearing and equilibrium. Additionally, it discusses common developmental abnormalities, including congenital deafness and external ear defects.

2. INTRODUCTION
 Anatomical unit serving both hearing and equilibrium
 In the embryo
1. the external ear
2. the middle ear
3. the inner ear

3. INTERNAL EAR

4. Internal ear
 Approximately 22 days – first indication
 Optic placodes invaginate and form otic or auditory
vesicles
 Each ventricle divides into
1. ventral component - saccule and cochlear duct
2. dorsal component – utricle, semicircular canals and
endolymphatic duct

5. Saccule, Cochlea and Organ of corti
 Tubular outpocketing at its lower pole
 It penetrates the surrounding mesenchyme in spiral
fashion. – 8 weeks, 2.5 turns.
 Differentiation into cartilage.
 Scala vestibuli and scala tympani are formed
 Vestibular memrane and basilar membrane

7. Saccule, Cochlea and Organ of corti
 Lateral wall – spiral ligament – surrounding cartilage
 Median angle – modiolus, the future axis of the bony
cochlear
 Inner ridge – the future spiral limbus
 Outer ridge – hair cells, the sensory cells of the
auditory system.

8. Organ of corti
 Sensory cells + tectorial membrane
 Impulses are transmitted to the spiral ganglion and
then to the nervous system by the auditory fibres
cranial nerve VIII

9. Utricle and semicircular canals
 During sixth week of development, semicircular canals
appear as flattened outpocketings of the reticular part
of the otic vesicle.
 Cels in ampulla – crista ampullaris containing sensory
cells for maintenance of equilibrium.
 Maculae acusticae develop in the walls of the utricle
and saccule.

11. Utricle and semicircular canals
 Impulses are carried to the brain by vestibular fibres of
cranial nerve VIII
 Statoacoustic ganglion – small group of cells breaks
away from its wall.
 Ganglion splits into cochlear and vestibular portions.

12. MIDDLE EAR
TYMPANIC CAVITY AND AUDITORY MEATUS
 1st pharyngeal pouch
 Contact with 1st pharyngeal cleft
 Distal part – primitive tympanic cavity
 Proximal part – auditory tube

13. Ossicles
 Malleus and incus - 1st pharyngeal pouch
 Stapes - 2nd pharyngeal pouch
 Remain embedded in the mesenchyme until 8th
month
 Tympanic cavity becomes twice its original size
 Endoderm epithelium connects ossicles to the wall of
the cavity in mesentary like fashion.
 Supporting ligaments of ossicles develop later.

14. Ossicles
 During late fetal life, by vacuolization of surrounding
tissue form tymapnic antrum.
 After birth – pneumatization
 Later, most of the mastoid air sinus come in contact
with the antrum and tympanic cavity – middle ear
infection.

15. EXTERNAL EAR
EXTERNAL AUDITORY MEATUS
 1st pharyngeal cleft
 At the beginning of 3rd month – medial plug is formed
 In the 7th month – plug dissolves and epithelial lining
of floor help in definitive eardrum formation

16. Eardrum or tympanic membrane
 Eardrum consists of
a) An ectodermal epithelial lining
b) An intermediate layer of mesenchyme
c) An endodermal lining which form the fibrous
strature.

17. Auricle
 Six mesenchymal proliferations
 These swellings, auricular hillocks later fuse and form
the definitive auricle.
 Developmental abnormalities of the auricle are
common
 Initially the external ears are in the lowerneck region
but later ascend to the side of the head at the level of
eye.

18. Clinical anatomy
CONGENITAL DEAFNESS
 Usually associated with deaf mutism

19. Clinical anatomy
EXTERNAL EAR DEFECTS
 They are common, they include minor and severe
abnormalities

20. Clinical anatomy
PREAURICULAR APPENDAGES AND PITS
 Pits indicate abnormal development of auricular
hillocks
 Appendages indicate abnormal development of
accessory hillocks