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The root of the neck | Main Anatomy Index | Neck Index
| The thyroid gland
Last updated 1 April 2006
- This is between the pharynx and the trachea. It communicates with the mouth and the nose
though the laryngeal and oral parts of the pharynx.
- Although it is part of the air passages, the larynx normally acts as a valve for
preventing swallowed food and foreign bodies from entering the lower respiratory passages.
- The larynx is the phonating mechanism that is
specifically designed for voice production.
- The larynx is located in the anterior portion of the neck.
- In adult males it is about 5 cm in length and is related posteriorly to the bodies of C3
to C6 vertebrae.
- The larynx is shorter in women and children and is situated slightly more superiorly in
The Skeleton of the
- The laryngeal skeleton comprises nine cartilages that are joined by various ligaments
- Three of the cartilages are single (thyroid, cricoid and epiglottis), and three are
paired (arytenoid, corniculate, and cuneiform).
The Thyroid Cartilage (p. 838)
- This is the largest of the laryngeal cartilages.
- It is composed of two laminae (L. thin plates).
- The inferior 2/3 of these laminae are fused anteriorly in the medial plane to form a
projection called the laryngeal prominence.
- The larynx is more prominent in postpubertal males than in females because the angle at
which the thyroid laminae meet is smaller in males. Also the anteroposterior diameter of
the laminae is greater.
- Immediately superior to the laryngeal prominence is a V-shaped
- The posterior border of each lamina projects superiorly as the superior
horn and inferior as the inferior horn (L. cornua).
- The superior border of the thyroid cartilage is attached to the hyoid
bone by the thyrohyoid membrane.
- An oblique line marks the lateral surface of each
lamina. It provides attachment for the inferior constrictor muscle of the pharynx and the
sternothyroid and thyrohyoid muscles.
- The inferior horns of the thyroid cartilage articulate with the cricoid cartilage at
special facets that allow the thyroid cartilage to tilt or glide anteriorly or posteriorly
in a visor-like manner.
The Cricoid Cartilage (p. 838)
- The cricoid (G. ring) is shaped like a signet ring with
its band facing anteriorly.
- The posterior (signet) part of the cricoid is called the lamina
and the anterior (band) part is termed the arch.
- Although it is much smaller than the thyroid cartilage, the cricoid is thicker and
- It is located at the level of C6 vertebra.
- It is the most inferior of the cartilages of the larynx.
- The cricoid forms the inferior parts of the anterior and lateral walls and most of the
posterior wall of the larynx.
- The cricoid cartilage is attached to the inferior margin of the thyroid cartilage by the
cricothyroid ligaments and to the first tracheal ring by
the cricotracheal ligament.
The Arytenoid Cartilages
- These paired cartilages are shaped like three-side pyramids.
- They articulate with the lateral parts of the superior border of the lamina of the
- Each cartilage has an apex superiorly, a vocal process anteriorly, and a muscular
- The apex is attached to the aryepiglottic fold, the vocal process to the vocal ligament,
and the muscular process to the posterior and lateral cricoarytenoid muscles.
Corniculate and Cuneiform Cartilages (pp. 838, 841)
- These are small cartilaginous nodules.
- They are in the posterior part of the aryepiglottic folds.
- These cartilages are attached to the apices of the arytenoid cartilages.
- The cuneiform (L. wedge-shaped) cartilages lie in the aryepiglottic folds and are
approximated to the tubercle of the epiglottis when the inlet of the larynx is closed
The Epiglottic Cartilage
- This is a thin piece of cartilage that is shaped like a leaf or a bicycle saddle.
- It gives flexibility to the epiglottis.
- It is situated posterior to the root of the tongue and hyoid bone and anterior to the
inlet of the larynx.
- The epiglottic cartilage forms the superior part of the anterior wall and the superior
margin of the inlet of the larynx.
- Its broad superior end is free, and its tapered inferior end is attached to the
thyroepiglottic ligament, located in the angle formed by the thyroid laminae.
- The anterior surface of the epiglottic cartilage is attached to the hyoid bone by the hyoepiglottic ligament.
- The inferior part of the posterior surface of the epiglottic cartilage that projects
posteriorly is called the epiglottic tubercle.
Joints of the Larynx
The Cricothyroid Joints (p.
- These articulations are located between the facets on the lateral surfaces of the
cricoid cartilage and the inferior horns of the thyroid cartilage.
- Each joint has a fibrous capsule, which is lined by a synovial membrane.
- The main movements at these joints are rotating and gliding of the thyroid cartilage.
- These movements result in the change in the length of the vocal folds.
- They also slacken or tighten the vocal ligaments, which pass between the arytenoid
cartilages and the thyroid cartilage.
The Cricoarytenoid Joints
- These articulations are located between the bases of the arytenoid cartilages and the
superior sloping surfaces of the lamina of the cricoid cartilage.
- These joints permit the following movements of the arytenoid cartilages: (1) sliding
toward or away from one another; (2) tilting anteriorly and posteriorly; and (3) rotary
- These movements are important in approximating, tensing, and relaxing the vocal folds.
Ligaments and Membranes
The Thyrohyoid Membrane (p.
- This is an extrinsic membrane that connects the thyroid cartilage to the hyoid bone,
thereby suspending the larynx.
- It is separated from the posterior surface of the body of the hyoid by a bursa.
- Its thicker median part is called the medial thyrohyoid ligament
and its thickened lateral parts are called the lateral thyrohyoid
- The lateral ligaments connect the tips of the superior horns of the thyroid cartilage to
the tips of the greater horn of the hyoid bone.
Cricothyroid and Cricotracheal Ligaments (p. 841)
- These ligaments connect the arch of the cricoid cartilage with the thyroid cartilage and
the first tracheal ring, respectively.
- The fibrous medial cricothyroid ligament produces a
soft spot inferior to the thyroid cartilage. At this point, the airway is closest to the
skin and most accessible.
Vocal Ligament, Vocal Fold, and Conus Elasticus (p. 842)
- The elastic vocal ligament extends from the junction of
the laminae of the thyroid cartilage anteriorly to the vocal process of the arytenoid
- The vocal ligaments form the skeleton of the vocal fold
and the free edge of the conus elasticus (cricothyroid
ligament), which is an elastic membrane that extends superiorly from the cricoid cartilage
to the vocal ligament.
- Note: cricothyroid ligament or membrane = cricovocal ligament = 1/2 conus elasticus (Grant's
Method of Anatomy 8th Ed).
Quadrangular Membrane and Vestibular Ligament (p. 842)
- This is a thin, submucosal sheet of connective tissue.
- It extends from the arytenoid cartilage to the cartilage of the epiglottis.
- Its free inferior margin constitutes the vestibular ligament,
which is loosely covered by a vestibular fold of mucous
- This fold lies superior to the vocal fold and extends from the thyroid cartilage to the
- The cricothyroid ligament and quadrangular membrane, although separated by the interval
between the vocal and vestibular ligaments, are referred to as the fibroelastic
membrane of the larynx.
Ligaments of the
Epiglottis (p. 842)
- The epiglottis is attached to the hyoid bone by the hyoepiglottic ligament.
- To the posterior part of the tongue by the median glossoepiglottic fold.
- To the sides of the pharynx by the lateral glossoepiglottic folds.
- To the thyroid cartilage by the thyroepiglottic ligament.
- The mucous membrane covering the epiglottis is reflected to the posterior part of the
tongue as one medial and two lateral glossoepiglottic folds.
Between these folds are depressions called epiglottic valleculae.
The Interior of the
- The cavity of the larynx extends from the inlet of the larynx,
through which it communicates with the laryngopharynx, to the level of the inferior border
of the cricoid cartilage, where it is continuous with the cavity of the trachea.
- The superior and inferior projecting folds of mucous membrane on each side, called the vestibular folds divide the larynx into three
- Superior to the vestibular folds, the cavity is called the vestibule
of the larynx.
- Between the vestibular folds, superior to the vocal folds is the ventricle
of the larynx.
- This is the smallest of the three cavities of the larynx.
- It extends laterally between the two folds as the sinus of the
- From each sinus, a saccule of the larynx passes
superiorly between the vestibular fold and the thyroid lamina.
- The inferior compartment of the larynx is called the infraglottic
- It extends from the vocal folds to the inferior border of the cricoid cartilage, where
it is continuous with the cavity of the trachea.
The Vocal Folds (pp. 843-4)
- The vocal folds (vocal cords) are concerned with the production of
- The apex of each wedge-shaped vocal fold projects medially into the laryngeal cavity,
and its base lies against the lamina of the thyroid cartilage.
- Each vocal fold consists of the vocal ligament, the conus elasticus, muscle fibres, and
a covering of mucous membrane.
- The rima glottidis is the aperture between the vocal
- The term glottis refers to the vocal folds, the rima
glottidis, and the narrow part of the larynx at the level of the vocal folds.
- The glottis is the part of the larynx most concerned with sound
- The shape of the rima glottidis varies according to the position of the vocal folds.
- During ordinary breathing, it is narrow and wedge-shaped; during forced respiration, it
- The vocal folds are closely approximated during speaking so that the rima glottidis
appears as a linear slit.
The Vestibular Folds (p. 844)
- These folds extend between the thyroid and arytenoid cartilages and play
little or no part in voice production.
- They consist of two thick folds of mucous membrane enclosing the vestibular ligaments.
- The space between the vestibular ligaments is called the rima
- The vestibular folds are part of the protective mechanism by which the larynx is closed
during swallowing to prevent the entry of food and foreign particles into it.
Muscles of the Larynx
Extrinsic Muscles (pp. 844-5)
Intrinsic Muscles (pp. 845)
- The intrinsic muscles are concerned with the movements of the
laryngeal parts, making alterations in the length and tension of the vocal
folds and in the size and shape of the rima glottidis in voice production.
- All intrinsic muscles of the larynx are supplied by the recurrent
laryngeal nerve, a branch of the vagus
nerve (CN X) except the cricothyroid muscle, which is
supplied by the external laryngeal nerve.
Adductors of the Vocal Folds
- The lateral cricoarytenoid muscles arise from the
lateral portions of the cricoid cartilage and inserts into the muscular processes or the
- These pull the muscular processes anteriorly, rotating the arytenoid cartilages so that
their vocal processes swing medially.
- These movements adduct the vocal folds and close the rima glottidis.
Abductors of the Vocal Folds
(pp. 845, 847)
- The principle abductors are the posterior cricoarytenoid muscles.
- These muscles arise on each side from the posterior surface of the lamina of the cricoid
cartilage and pass laterally and superiorly to insert into the muscular processes of the
- They rotate the arytenoid cartilages, thereby deviating them laterally and widening the
Tensors of the Vocal Folds (p.
- The main tensors are the triangular cricothyroid muscles.
- These are located on the external surface of the larynx between the cricoid and thyroid
- The muscle on each side arises from the anterolateral part of the cricoid cartilage and
inserts into the inferior margin and anterior aspect of the inferior horn of the thyroid
- These muscles tilt the thyroid cartilage anteriorly on the cricoid cartilage, increasing
the distance between the thyroid and arytenoid cartilages.
- As a result, the vocal ligaments are elongated and tightened and the pitch of the voice
Relaxers of the Vocal Folds
- The principle relaxers of these folds are the broad thyroarytenoid
- They arise from the posterior surface of the thyroid cartilage near the median plane and
insert into the anterolateral surfaces of the arytenoid cartilages.
- One band of its inferior deep fibres, called the vocalis muscle,
arises from the vocal ligament and passes to the vocal process of the arytenoid cartilages
- The thyroarytenoid muscles pull the arytenoid cartilages anteriorly, thereby slackening
the vocal ligaments.
- The vocalis muscles produce minute adjustments of the vocal
ligaments (e.g., as occurs during whispering). They also relax parts of the
vocal folds during phonation and singing.
Blood Supply of the
Larynx (p. 847)
- The superior and inferior laryngeal arteries supply the
- They are branches of the superior and inferior thyroid arteries respectively.
- The superior laryngeal
artery runs with the internal branch of the superior laryngeal nerve through
the thyrohyoid membrane, and then branches to supply the internal surface of the larynx.
- The inferior laryngeal
artery runs with the inferior laryngeal nerve and supplies the mucous membrane
and muscles of the inferior aspect of the larynx.
Innervation of the
Larynx (p. 848-9)
- The laryngeal nerves are derived from the vagus
nerve (CN X) through the superior laryngeal nerve and the
recurrent laryngeal nerve.
- All intrinsic muscles, except cricothyroid, are innervated by the recurrent
laryngeal nerve with fibres from the accessory nerve (CN XI). The external laryngeal nerve supplies the cricothyroid muscle.
- The supraglottic portion of the laryngeal
mucosa is supplied by the internal laryngeal nerve,
a branch of the superior laryngeal nerve.
- The infraglottic portion of the laryngeal mucosa is
supplied by the recurrent laryngeal nerve.
Drainage of the Larynx (p. 849)
- The lymph vessels superior to the vocal folds accompany
the superior laryngeal artery through the thyrohyoid membrane and drain into the superior deep cervical lymph nodes.
- The lymph vessels inferior to the vocal folds drain
into the inferior deep cervical lymph nodes
(supraclavicular nodes) through the prelaryngeal, pretracheal, and paratracheal lymph