J Am Acad Audiol 8 : 379-382 (1997)
Development of the Human External Ear
C. Gary Wright*
Abstract
External ear development is a lengthy and complex process that extends from early embryonic life until well into the postnatal period . Initial development of the auricle and external
auditory canal during the fourth and fifth weeks of gestation is closely associated with anatomical changes involving the pharyngeal arch apparatus of the human embryo . The auricle and
external canal are well formed by the time of birth but do not attain their full size and adult
configuration until about 9 years of age. Sebaceous and modified apocrine glands, which
are responsible for cerumen production, begin their development at about 5 months gestation in association with hair follicles in the outer portion of the external canal. Although they
appear anatomically mature before birth, these glands do not reach full functional capacity
until puberty.
Key Words:
Auricle, embryological development, external auditory canal
s emphasized throughout this special
issue, the external ear plays an essential
Arole in auditory function and occupies an
important place in the clinical practice of audiology and otology. Its major components, the
auricle and external auditory canal, receive
sound energy from the environment and provide
some degree of directional and frequency selectivity for the incoming sound stimulus . They
also serve to protect the tympanic membrane
from mechanical injury and from abrupt changes
in temperature and humidity. Various abnormalities affecting the external ear, particularly
those involving congenital defects, are best
understood from a developmental perspective .
This article offers a brief overview of pre- and
postnatal development of the external ear to
serve as a point of departure for further discussion of its anatomy, physiology, and pathology.
External ear development is a process that
begins in embryonic life, progresses through
the fetal period to the time of birth, and continues
postnatally until the age of puberty, when the
glands of the external canal become fully functional . (As usually defined, the embryonic phase
of human development extends from 2 weeks gestational age up to the seventh or eighth week,
*Callier Center for Communication Disorders, University of Texas at Dallas, and the Department of Otorhinolaryngology, University of Texas Southwestern Medical
Center, Dallas, Texas
Reprint requests: C.G . Wright, Callier Center for Communication Disorders, 1966 Inwood Rd ., Dallas, TX 75235
while the fetal period is the interval from about
8 weeks gestation to term .)
The embryonic pharyngeal arch apparatus
provides the structural foundation for formation
of the external ear. As illustrated in Figure 1, the
pharyngeal arches are conspicuous external features of the human embryo and are significantly
involved in various aspects of head and neck
development. The arches are obliquely oriented,
rounded ridges separated by prominent grooves
or clefts . They correspond to the gill-bearing
branchial arches of fishes that are separated
by clefts through which water flows for delivery
of oxygen to the gills . In mammalian embryos,
the pharyngeal arch apparatus never assumes
a respiratory function and no communication is
normally established between the pharynx and
the pharyngeal clefts as occurs in the branchial
arch system of fishes . The clefts do, however,
come into close relationship with outpocketings
of the pharynx known as the pharyngeal
pouches. In fact, it is the first of these pouches
that eventually elongates to form the tubotympanic recess, from which the eustachian tube and
middle ear cavity develop.
By the end of the fourth week of gestation,
four well-defined pairs of pharyngeal arches are
externally visible in the neck region of the human
embryo (see Fig. 1) . The first two of these, the
mandibular and hyoid arches, are important
contributors to external ear development. During the fifth gestational week, nodular swellings
of tissue known as the hillocks of His appear on
the first and second pharyngeal arches . Six such
379
Journal of the American Academy of Audiology/Volume 8, Number 6, December 1997
otic vesicle
wall of hindbrain
otic vesicle
derl, .ties of the
fingarch cartilage
First
pharyngeal
primitive
"'j~1r~ .
wborympanic
recast
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and
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-~ty,paaic
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Figure 3 Schematic drawings illustrating cross-sections
of the embryonic and fetal head at various stages in the
development of the external acoustic meatus (or external earcanal, EAC) . A and B show the relationship of the
first pharyngeal cleft (also known as the first branchial
groove as labelled here) to the first pharyngeal pouch at
Figure 1 Semi-schematic drawings showing lateral
(A) and frontal (B) views of a human fetus at approximately 4.5 weeks gestational age. The four pharyngeal
arches visible at this stage of development are numbered 1 through 4, with numbers 1 and 2 being the
mandibular and hyoid arches, respectively. The arrow indicates the first pharyngeal cleft; OV = otic vesicle (precursor
of the inner ear) .
hillocks, three on either side of the first pharyngeal cleft, can be distinguished . Most investigators believe that the auricle is formed by
growth, differentiation, and fusion of these six
tissue condensations . There is some disagreement, however, as to the exact adult structures
that form from the auricular hillocks . The diagram shown in Figure 2 illustrates one widely
Cymba conchae
Conch .
Antihelix
Antitragus
Figure 2 A, lateral view of the head of an embryo
showing the six auricular hillocks (hillocks of His) surrounding the dorsal end of the first pharngeal cleft. B, C,
and D illustrate the fusion and progressive development
of the hillocks into the adult auricle. (Reprinted with
permission : Sadler TW. (1985) . Langman's Medical
Embryology . 5th ed . Baltimore: Williams and Wilkins.)
380
4 (A) and 5 (B) weeks gestational age. C illustrates the
meatal plug filling the deep portion of the EAC at 8 to
10 weeks gestational age. D shows the fully formed
earcanal after disappearance of the meatal plug .
(Reprinted with permission : Moore KL, Persaud TVN.
(1993) . The Developing Human: Clinically Oriented
Embryology . 5th ed. Philadelphia : WB Sounders .)
held view on the origin of the various parts of
the auricle. During the initial stages of its development, the auricle is located in the general
area of the neck, behind the lower jaw, but by
the 20th week of gestation it has moved upward
to attain its adult location and overall configuration . In a 4- to 5-year-old child, the auricle is
about 80 percent adult size . It reaches full adult
size by approximately 9 years of age.
A short time after the appearance of the
hillocks of His on the first and second pharyngeal arches, the upper or dorsal portion of the
first pharyngeal cleft deepens as shown in Figure 3 to form a funnel-shaped depression that
is the precursor of the external auditory canal.
At 4 to 5 weeks gestation, the primitive external canal establishes contact with the first pharyngeal pouch, as illustrated in Figure 3A . This
contact is soon lost due to proliferation of embryonic connective tissue, which separates the two
structures . In the eighth week, the developing
external canal deepens further to once again
approach the middle ear space. Shortly thereafter, the ectodermal lining of the deep portion
of the primitive earcanal proliferates to form a
solid tissue structure called the meatal plate
(or meatal plug), which fills the medial portion
of the canal (see Fig. 3C). The meatal plate ends
in a rounded, disc-shaped swelling that lies
External Ear Development/Wright
Figure 4 Hair follicles with associated glands in the lateral portion of
the external auditory canal of a 22week gestational age human fetus. A,
a developing sebaceous gland (arrow)
budding from the upper portion of a
hair follicle . B, a differentiating modified apocrine gland (asterisk) with its
secretory duct (arrow) entering a hair
follicle. EP = epidermis on the surface
of the earcanal . Original magnification 75x .
immediately adjacent to the middle ear. According to some accounts of external ear development, the meatal plate remains intact until the
21st to 28th week of gestation, when it hollows
out due to maturational changes affecting its central cells. Continued canalization of the meatal
plate produces the medial two-thirds of the
definitive external auditory canal. The innermost
portion of the meatal plate becomes the outer
layer of the tympanic membrane .
Recent evidence indicates that canalization
of the meatal plate may occur considerably earlier in gestation than is widely believed . In a
recent study that focused on this question,
Nishimura and Kumoi (1992) found that the
meatal plate begins to open during the 13th
week of gestation and that the external canal is
fully patent throughout its entire length in the
18-week fetus. These findings are also consistent
with earlier observations from Anson and Donaldson (1973) . The timing of canalization of the
meatal plate is therefore not yet fully resolved
and is an aspect of external auditory canal development that needs further study.
As noted above, the outer, or epidermal,
layer of the tympanic membrane is derived from
the ectoderm of the meatal plate. The inner
layer, facing the middle ear cavity, is a derivative
Figure 5 Later stages of external
auditory canal gland development.
A, sebaceous glands (arrows) attached
to a hair follicle in a 28-week gestational age human fetus. Original
magnification 100x . B, coiled tubules
of a modified apocrine gland (star) in
a 1-year-old infant . The secretory
duct (arrow) of the gland is seen opening into a hair follicle . Original magnification 75x.
381
Journal of the American Academy of Audiology/Volume 8, Number 6, December 1997
of the first pharyngeal pouch and the intermediate layer develops as a condensation of embryonic
connective tissue (mesenchyme) that separates
the inner and outer layers . The three-layered
structure of the tympanic membrane is illustrated diagramatically in Figure 3D .
At the time of birth, the tympanic membrane is nearly horizontal in orientation and
the external canal is short (about 20 mm long)
and straight . The tympanic membrane reaches
its definitive, more vertical position of 50 to 60
degrees from horizontal during the third year of
life and, by that time, bone formation around the
inner two-thirds of the external canal is nearly
complete . The earcanal itself continues to elongate and increase its curvature until about 9
years of age.
Hair follicles in the outer one-third of the
external auditory canal make their appearance
rather early in the course of development at
approximately 17 weeks of gestation. There is
little information in the available literature
specifically regarding fetal development of the
glands of the external auditory canal that are
responsible for cerumen production . However,
in a study completed some 60 years ago, Simonetta and Magnoni (1937) describe the appearance of sebaceous glands at the 17-week stage
in close association with developing hair follicles . According to these investigators, modified
apocrine glands (the so-called ceruminous
glands) are recognizable shortly thereafter. Figure 4 illustrates developing sebaceous and modified apocrine glands in a human earcanal at 22
weeks gestation. The more mature configuration of these glands is shown in Figure 5 . Both
types of glands appear structurally complete by
6 months gestational age . However, they do
not reach full functional capacity until the time
of puberty.
Acknowledgment. The author is grateful to Karen S.
Pawlowski for the drawings used in Figure 1 and for
histologic processing of the tissue specimens shown in Figures 4 and 5.
REFERENCES
Anson BJ, Donaldson JA. (1973) . Surgical Anatomy of
the Temporal Bone and Ear. 2nd ed . Philadelphia : WB
Saunders .
Nishimura Y, Kumoi T. (1992) . The embryonic development of the human external auditory meatus . Acta
Otolaryngol112 :496-503 .
Simonetta B, Magnoni A. (1937) . Lo sviluppo delle ghiandole sebacee e ceruminose del condatto uditivo esterno
nell'uomo. Arch Ital Anat e Embriol 39 :245-261 .
SUGGESTED ADDITIONAL READINGS
Kenna MA . (1990) . Embryology and developmental
anatomy of the ear. In : Bluestone CD, Stool SE, eds.
Pediatric Otolaryngology . 2nd ed . Philadelphia : WB
Saunders, 77-87.
Larsen WJ . (1993) . Human Embryology . New York :
Churchill Livingstone.
Moore EL, Persaud TVN. (1993) . The Developing Human:
Clinically Oriented Embryology . 5th ed . Philadelphia :
WB Saunders .
Pearson AA, Jacobson AD, Van Calcar RJ, Sauter RW.
(1970) . The Development of the Ear. Rochester, MN :
American Academy of Ophthalmology and Otolaryngology.
Sadler TW. (1985) . Langman's Medical Embryology . 5th
ed . Baltimore : Williams and Wilkins .
Schuknecht HF, Gulya AJ . (1986) . Anatomy of the
Temporal Bone with Surgical Implications . Philadelphia :
Lea and Febiger.
Sulik KK . (1995) . Embryology of the ear. In : Gorlin RJ,
Toriello HV, Cohen MM Jr., eds. Hereditary Hearing Loss
and Its Syndromes . Oxford Monographs on Medical
Genetics No . 28 . New York : Oxford University Press,
22-42 .