Larynx

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CHAPTER 34 Larynx

The larynx is an air passage, a sphincter and an organ of phonation, and extends from the tongue to the trachea. It projects ventrally between the great vessels of the neck and is covered anteriorly by skin, fasciae and the hyoid depressor muscles. Above, it opens into the laryngopharynx and forms its anterior wall; below, it continues into the trachea (see Fig. 33.2). It is mobile on deglutition. At rest, the larynx lies opposite the third to sixth cervical vertebrae in adult males; it is somewhat higher in children and adult females. In infants between 6 and 12 months, the tip of the epiglottis (the highest part of the larynx) lies a little above the junction of the dens and body of the axis vertebra. Until puberty, male and female larynges are similar in size. After puberty, the male larynx enlarges considerably in comparison with that of the female: all the cartilages increase in both size and weight, the thyroid cartilage projects in the anterior midline of the neck, and its sagittal diameter nearly doubles. The male thyroid cartilage continues to increase in size until 40 years of age, after which no further growth occurs.

SKELETON OF THE LARYNX

The skeletal framework of the larynx is formed by a series of cartilages interconnected by ligaments and fibrous membranes, and moved by a number of muscles (Figs 34.1–34.3). The hyoid bone is attached to the larynx: it is usually regarded as a separate structure with distinctive functional roles, and is described on page 436. The laryngeal cartilages are the single thyroid, cricoid and epiglottic cartilages, and the paired arytenoid, cuneiform, corniculate and tritiate cartilages.

Fig. 34.1 Anterolateral view of the laryngeal cartilages and ligaments.

Fig. 34.2 Posterior view of the laryngeal cartilages and ligaments.

Fig. 34.3 Cartilages of the larynx: thyroid (A), cricoid (B), arytenoid (C), epiglottis (D), cricoarytenoid joint (E). The attachments of the false vocal folds (vestibular ligaments) (above) and the true vocal folds (vocal ligaments) (below) are shown in A, posterior aspect. Note the pitted surface of the epiglottis (D).

In relation to the surface anatomy of the larynx, the levels of the laryngeal cartilages worth noting are: C3 (level of body of hyoid and its greater cornu); C3–4 junction (level of upper border of thyroid cartilage and bifurcation of common carotid artery); C4–5 junction (level of thyroid cartilage); C6 (level of cricoid cartilage).

The corniculate, cuneiform, tritiate and epiglottic cartilages and the apices of the arytenoid are composed of elastic fibrocartilage, with little tendency to calcify. The thyroid, cricoid and the greater part of the arytenoid cartilages consist of hyaline cartilage and may undergo mottled calcification as age advances, starting about the 25th year in the thyroid cartilage and somewhat later in the cricoid and arytenoids. By the 65th year, these cartilages commonly appear patchily dense in radiographs.

EPIGLOTTIS

The epiglottis is a thin leaf-like plate of elastic fibrocartilage which projects obliquely upwards behind the tongue and hyoid body, and in front of the laryngeal inlet (Figs 34.2, 34.3; see Fig. 34.5). Its free end, which is broad and round, and occasionally notched in the midline, is directed upwards. Its attached part, or stalk (petiolus), is long and narrow and is connected by the elastic thyroepiglottic ligament to the back of the laryngeal prominence of the thyroid cartilage just below the thyroid notch. Its sides are attached to the arytenoid cartilages by aryepiglottic folds (which contain the aryepiglottic muscle). Its free upper anterior, or lingual, surface is covered by mucosa (the epithelium is non-keratinized stratified squamous), which is reflected onto the pharyngeal aspect of the tongue and the lateral pharyngeal walls as a median glossoepiglottic, and two lateral glossoepiglottic, folds. There is a depression, the vallecula, on each side of the median fold. The lower part of its anterior surface, behind the hyoid bone and thyrohyoid membrane, is connected to the upper border of the hyoid by an elastic hyoepiglottic ligament, and separated from the thyrohyoid membrane by adipose tissue, which constitutes the clinically important preepiglottic space. The smooth posterior, or laryngeal, surface is transversely concave and vertically concavo-convex, and is covered by ciliated respiratory mucosa: its lower projecting part is called the tubercle. This surface forms the oblique anterior wall of the laryngeal vestibule. The cartilage is posteriorly pitted by small mucous glands (Fig. 34.3D) and is perforated by branches of the internal laryngeal nerve and fibrous tissue, which means that the posterior surface of the epiglottis is in continuity through these perforations with the pre-epiglottic space.

Fig. 34.5 A and B, Sagittal sections of the left side of the larynx, showing the laryngeal membranes (A) and the interior aspect (B) of the left half of the larynx. C, The quadrangular membrane viewed from the left side.

(A, From Drake, Vogl and Mitchell 2005.)

Functions of the epiglottis

During swallowing, the hyoid bone moves upwards and forwards, and the epiglottis is bent posteriorly as a result of passive pressure from the base of the tongue and active contraction of the aryepiglottic muscles. Though the epiglottis is not essential to swallowing, which can occur with minimal aspiration even if the epiglottis is destroyed by disease, it diverts food and liquids away from the laryngeal inlet and into the lateral food channels. It is not essential for respiration or phonation.

THYROID CARTILAGE

The thyroid cartilage is the largest of the laryngeal cartilages (Figs 34.1–34.3). It consists of two quadrilateral laminae with anterior borders that fuse along their inferior two-thirds at a median angle to form the subcutaneous laryngeal prominence (‘Adam’s apple’). This projection is most distinct at its upper end, and is well marked in men but scarcely visible in women. Above, the laminae are separated by a V-shaped superior thyroid notch or incisure. Posteriorly, the laminae diverge, and their posterior borders are prolonged as slender horns, the superior and inferior cornua. A shallow ridge, the oblique line, curves downwards and forwards on the external surface of each lamina: it runs from the superior thyroid tubercle lying a little anterior to the root of the superior cornu, to the inferior thyroid tubercle on the inferior border of the lamina. Sternothyroid, thyrohyoid and thyropharyngeus (part of the inferior pharyngeal constrictor) are attached to the oblique line, usually as little more than a tendon (Fig. 34.3A).

The internal surface of the lamina is smooth. Above and behind, it is slightly concave and covered by mucosa. The thyroepiglottic ligament, the paired vestibular and vocal ligaments, the thyroarytenoid, thyroepiglottic and vocalis muscles, and the stalk of the epiglottis are all attached to the inner surface of the cartilage, in the angle between the laminae. The true vocal folds lie 6–9 mm below the median thyroid notch. The superior border of each lamina is concave behind and convex in front, and the thyrohyoid membrane is attached along this edge (Figs 34.1, 34.2). The inferior border of each lamina is concave behind and nearly straight in front, and the two parts are separated by the inferior thyroid tubercle. Anteriorly, the thyroid cartilage is connected to the cricoid cartilage by the anterior (median) cricothyroid ligament, which is a thickened portion of the cricothyroid membrane.

The anterior border of each thyroid lamina fuses with its partner at an angle of approximately 90° in men and approximately 120° in women. The shallower angle in men is associated with the larger laryngeal prominence, the greater length of the vocal cords, and the resultant deeper pitch of the voice. The posterior border is thick and rounded and receives fibres of stylopharyngeus and palatopharyngeus. The superior cornu, which is long and narrow, curves upwards, backwards and medially, and ends in a conical apex to which the lateral thyrohyoid ligament is attached. The inferior cornu is short and thick, and curves down and slightly anteromedially. On the medial surface of its lower end there is a small oval facet for articulation with the side of the cricoid cartilage: this facet is variable and is well defined only sometimes.

During infancy, a narrow, rhomboidal, flexible strip, the intra-thyroid cartilage, lies between the two laminae, and is joined to them by fibrous tissue.

CRICOID CARTILAGE

The cricoid cartilage is attached below to the trachea, and articulates with the thyroid cartilage and the two arytenoid cartilages by synovial joints. It forms a complete ring around the airway, the only laryngeal cartilage to do so (Fig. 34.3B). It is smaller, but thicker and stronger, than the thyroid cartilage, and has a narrow curved anterior arch, and a broad, flatter posterior lamina.

Cricoid arch

The cricoid arch is vertically narrow in front (5–7 mm in height), and widens posteriorly towards the lamina. Cricothyroid is attached to the external aspect of its front and sides, and cricopharyngeus (part of the inferior pharyngeal constrictor) is attached behind cricothyroid. The arch is palpable below the laryngeal prominence, from which it is separated by a depression containing the resilient cricothyroid membrane. The inferior border of the cartilage is nearly horizontal and is circular in outline, whereas the upper border is more elliptical.

Cricoid lamina

The cricoid lamina is approximately quadrilateral in outline, and 2–3 cm in vertical dimension. It bears a posterior median vertical ridge that creates posterior concavities on either side. The two fasciculi of the longitudinal layer of oesophageal muscle fibres (muscularis externa) are attached by a tendon to the upper part of the ridge. Posterior cricoarytenoid attaches to a shallow depression on either side of the ridge.

A discernible circular synovial facet, facing posterolaterally, sometimes marks the junction of the lamina and arch: it indicates the site where the cricoid articulates with the inferior thyroid cornu. The inferior border of the cricoid is horizontal, and joined to the first tracheal cartilage by the cricotracheal ligament (Fig. 34.1). The superior border runs obliquely up and back, and gives attachment anteriorly to the thick median part of the cricothyroid membrane, and laterally to the membranous parts of the cricothyroid membrane (Fig. 34.1) and lateral cricoarytenoid. The posterosuperior aspect of the lamina presents a shallow median notch, on each side of which is a smooth, oval, convex facet, directed upwards and laterally, for articulation with the base of an arytenoid cartilage.

The internal surface of the cricoid cartilage is smooth and lined by mucosa.

Subglottic stenosis

Congenital malformation of the cricoid cartilage may result in severe narrowing of the subglottic airway and respiratory obstruction, which, in severe cases, is present from birth. It is the third most common congenital disorder of the larynx. Acquired subglottic stenosis is more common and is the result of trauma and scarring following prolonged endotracheal intubation for the purposes of ventilation of premature babies on intensive care units.

ARYTENOID CARTILAGE

The paired arytenoid cartilages articulate with the lateral parts of the superior border of the cricoid lamina (Figs 34.2, 34.3). Each is pyramidal, and has three surfaces, two processes, a base and an apex. The posterior surface, which is triangular, smooth and concave, is covered by transverse arytenoid. The anterolateral surface is convex and rough, and bears, near the apex of the cartilage, an elevation from which a crest curves back, down and then forwards to the vocal process. The lower part of this arcuate crest separates two depressions (foveae). The upper is triangular (fovea triangularis), and the vestibular ligament is attached to it. The lower is oblong (fovea oblonga), and vocalis and lateral cricoarytenoid are attached to it. The medial surface is narrow, smooth and flat, and is covered by mucosa: its lower edge forms the lateral boundary of the intercartilaginous part of the rima glottidis. The base is concave, with a smooth surface for articulation with the lateral part of the upper border of the cricoid lamina. Its round, prominent lateral angle, or muscular process, projects backwards and laterally: it gives attachment to posterior cricoarytenoid behind, and lateral cricoarytenoid in front. The vocal ligament is attached to its pointed anterior angle (vocal process), which projects horizontally forward. The apex curves backwards and medially and articulates with the corniculate cartilage.

CORNICULATE CARTILAGES

The corniculate cartilages are two conical nodules of elastic fibrocartilage which articulate with the apices of the arytenoid cartilages, prolonging them posteromedially (Fig. 34.3E). They lie in the posterior parts of the aryepiglottic mucosal folds, and are sometimes fused with the arytenoid cartilages.

CUNEIFORM CARTILAGES

The cuneiform cartilages are two small, elongated, club-like nodules of elastic fibrocartilage, one in each aryepiglottic fold anterosuperior to the corniculate cartilages, and are visible as whitish elevations through the mucosa (see Fig. 34.5).

TRITIATE CARTILAGES (CARTILAGO TRITICEA)

The tritiate cartilages are two small nodules of elastic cartilage, situated one on either side above the larynx within the posterior free edge of the thyrohyoid membrane, about halfway between the superior cornu of the thyroid cartilage and the tip of the greater cornu of the hyoid bone (Figs 34.1, 34.2). Their functions are unknown, although they may serve to strengthen this connection.

CALCIFICATION OF LARYNGEAL CARTILAGES

The thyroid, cricoid, and most of the arytenoid cartilages consist of hyaline cartilage, and may therefore become calcified. This process normally starts at about 18 years of age. Initially it involves the lower and posterior part of the thyroid cartilage, and subsequently spreads to involve the remaining cartilages, calcification of the arytenoid cartilage starting at its base. The degree and frequency of calcification of the thyroid and cricoid cartilages appear to be less in females. There is some evidence to suggest that a predilection for tumour invasion may be enhanced by calcification of the laryngeal cartilages.

The tip and upper portion of the vocal process of the arytenoid cartilage consists of non-calcifying, elastic cartilage. This may have considerable functional significance: the vocal process may bend at the elastic cartilage during adduction and abduction, and the two arytenoid cartilages will contact mainly at their ‘elastic’ superior portions during adduction.

JOINTS

CRICOTHYROID JOINT

The joints between the inferior cornua of the thyroid cartilage and the sides of the cricoid cartilage are synovial. Each is enveloped by a capsular ligament strengthened posteriorly by fibrous bands (Figs 34.1, 34.2, 34.4). Both capsule and ligaments are rich in elastin fibres. The primary movement at the joint is rotation around a transverse axis which passes transversely through both cricothyroid joints. The effect of this rotation is to move the cricoid and thyroid cartilages relative to one another in such a way as to bring together the lamina of the thyroid cartilage and the arch of the cricoid cartilage (‘closing the visor’). There is some controversy as to which cartilage moves, but it seems most likely that the cricoid cartilage rotates to a greater extent. When the joint is in a neutral position, the ligaments are slack and the cricoid can glide, to a limited extent, in different directions on the thyroid cornua. The effect of these movements is to lengthen the vocal folds, provided the arytenoid cartilages are stabilized at the cricoarytenoid joint. This may also increase vocal fold tension.

Fig. 34.4 A, Lateral view of the cricothyroid joint. B, Anterosuperior view of the cricoarytenoid joint.

CRICOARYTENOID JOINT

The cricoarytenoid joints are a pair of synovial joints between the facets on the lateral parts of the upper border of the lamina of the cricoid cartilage and the bases of the arytenoids. Each joint is enclosed by a capsular ligament and strengthened by a ligament that, although traditionally called the posterior cricoarytenoid ligament, is largely medial in position (Figs 34.1–34.4).

The cricoid facets are elliptical, convex and obliquely directed laterally, anteriorly and downwards. The long axes of the two facets intersect posteriorly at an angle of about 50°. Two movements occur at this joint. The first is rotation of the arytenoid cartilages at right angle to the long axis of the cricoid facet (dorso-medio-cranial to ventro-latero-caudal), which, because of its obliquity, causes each vocal process to swing laterally or medially, thereby increasing or decreasing the width of the rima glottidis. This movement is sometimes referred to as a rocking movement of the arytenoid cartilages. There is also a gliding movement, by which the arytenoids approach or recede from one another, the direction and slope of their articular surfaces imposing a forward and downward movement on lateral gliding. The movements of gliding and rotation are associated, i.e. medial gliding occurs with medial rotation and lateral gliding with lateral rotation, resulting in adduction or abduction of the vocal folds respectively. When viewed from above, foreshortening can give the illusion that the arytenoid cartilages are rotating about their vertical axes, but the shape of the facets prevents such movement occurring. The posterior cricoarytenoid ligaments limit forward movements of the arytenoid cartilages on the cricoid cartilage. It has been suggested that the ‘rest’ position of the cricoarytenoid ligament is a major determinant of the position of a denervated vocal cord.

ARYTENOCORNICULATE JOINTS

Synovial or cartilaginous joints link the arytenoid and corniculate cartilages.

INNERVATION OF THE CRICOTHYROID, CRICOARYTENOID AND ARYTENOCORNICULATE JOINTS

The cricothyroid, cricoarytenoid and arytenocorniculate joints are innervated by branches of the recurrent laryngeal nerves, which arise either independently or from branches of the nerve to the laryngeal muscles. The capsules of the laryngeal joints contain numerous lamellated (Pacinian) corpuscles, Ruffini corpuscles and free nerve endings.

SOFT TISSUES

The skeletal framework of the larynx is joined to surrounding structures by extrinsic membranes. It is also interconnected by intrinsic ligaments and fibroelastic membranes, of which the thyrohyoid, quadrangular and cricothyroid membranes and the conus elasticus are the most significant. The thyrohyoid membrane is external to the larynx, whereas the paired quadrangular membranes, the cricothyroid membrane and the conus elasticus are internal. The named ligaments are the median (anterior) cricothyroid ligament, the hyoepiglottic and thyroepiglottic ligaments and the cricotracheal ligament.

EXTRINSIC LIGAMENTS AND MEMBRANES

Thyrohyoid membrane

The thyrohyoid membrane is a broad, fibroelastic layer attached below to the superior border of the thyroid cartilage lamina and the front of its superior cornua, and above to the superior margin of the body and greater cornua of the hyoid (Figs 34.1, 34.2, 34.5). It thus ascends behind the concave posterior surface of the hyoid, separated from its body by a bursa which facilitates the ascent of the larynx during swallowing. Its thicker part is the median thyrohyoid ligament. The more lateral, thinner, parts are pierced by the superior laryngeal vessels and internal laryngeal nerves (Fig. 34.1). Externally, it is in contact with thyrohyoid and omohyoid and the body of the hyoid bone. Its inner surface is related to the lingual surface of the epiglottis and the piriform fossae of the pharynx. The round, cord-like, elastic lateral thyrohyoid ligaments form the posterior borders of the thyrohyoid membrane, and connect the tips of the superior thyroid cornua to the posterior ends of the greater hyoid cornua (Fig. 34.1).

The fibroelastic membrane of the larynx lies within the cartilaginous skeleton of the larynx, beneath the laryngeal mucosa (Fig. 34.5). It forms a discontinuous sheet separated on both sides of the larynx by a horizontal cleft between the vestibular and vocal ligaments. Its upper part, the quadrangular membrane, extends between the arytenoid cartilages and the sides of the epiglottis. Its lower part, the cricothyroid membrane and conus elasticus, connects the thyroid, cricoid and arytenoid cartilages.

Quadrangular membrane

Each quadrangular membrane passes from the lateral margin of the epiglottis to the ipsilateral arytenoid cartilage. It is often poorly defined, especially in its upper portion. The upper and lower borders of the membrane are free. The upper border slopes posteriorly to form the aryepiglottic ligament, which constitutes the central component of the aryepiglottic fold. Posteriorly, it passes through the fascial plane of the oesophageal suspensory ligament, and helps to form the median corniculopharyngeal ligament which extends into the submucosa adjacent to the cricoid cartilage. This ligament may exert vertical traction on the tissues of the laryngopharynx. The cuneiform cartilages lie within the aryepiglottic folds. The lower border of the quadrangular membrane forms the vestibular fold.

Cricothyroid membrane and the conus elasticus

The cricothyroid ligament is composed mainly of elastic tissue. It consists of two parts: the cricothyroid membrane below and the conus elasticus above.

Cricothyroid membrane and median (anterior) cricothyroid ligament

The cricothyroid membrane passes upwards from the upper border of the cricoid cartilage to the lower border of the thyroid cartilage. Anteriorly, it is thickened to form the median (anterior) cricothyroid ligament, which is broader below and narrower above.

Conus elasticus

In part or in whole, the conus elasticus has been variously described as the cricovocal membrane, cricothyroid ligament or lateral cricothyroid ligament. The conus elasticus is thinner than the anterior cricothyroid ligament. It arises beneath the cricothyroid membrane on both sides from the inner surface of the cricoid cartilage, near its lower margin, and passes upwards beneath the lower border of the thyroid cartilage. It is attached anteriorly to the inner surface of the angle of the thyroid cartilage (just below its midpoint) and posteriorly to the tip of the vocal process of the arytenoid cartilage. Between these attachments, the upper edge of the conus elasticus is free, horizontally aligned and thickened to form the vocal ligament, which lies within the mucosa-covered vocal fold. It is covered internally by mucosa and externally by lateral cricoarytenoid and thyroarytenoid. The conus elasticus derives its name from the cone or funnel shape produced by the superior and medial curving of its walls between its inferior and superior attachments. This is said to maximize efficient flow of air towards the rima glottidis during phonation.

LARYNGEAL CAVITY

The laryngeal cavity extends from the laryngeal inlet (from the pharynx) down to the lower border of the cricoid cartilage, where it continues into the trachea (Figs 34.5, 34.6). The walls of the cavity are formed of the fibroelastic membranes described above and are lined with mucous membrane which folds over the free edges of these fibroelastic membranes within the larynx. On either side, the continuity of the fibroelastic membrane is interrupted between the upper and lower folds.

Fig. 34.6 Coronal section through the larynx and the cranial end of the trachea: posterior aspect.

The folds project into the lumen of the cavity and divide it into upper and lower parts, separated by a middle portion between the two sets of folds leading into the laryngeal ventricle. The upper folds are the vestibular (ventricular or false vocal) folds; the median aperture which they guard is the rima vestibuli. The lower pair are the (true) vocal folds (or vocal cords), and the fissure between them is the rima glottidis or glottis. The true vocal folds are the primary source of phonation, whereas the vestibular folds normally do not contribute directly to sound production. The clinical term supraglottis refers to the part of the larynx that lies above the glottis and comprises the laryngeal inlet formed of the laryngeal surface of the epiglottis and arytenoid cartilages and the laryngeal aspects of the aryepiglottic folds, the laryngeal vestibule (introitus) and the vestibular folds.

MICROSTRUCTURE OF THE LARYNX

The laryngeal mucosa is continuous with that of the pharynx above and the trachea below. It lines the entire inner surface of the larynx, including the ventricle and saccule, and is thickened over the vestibular folds, where it is the chief component. Over the vocal folds it is thinner, and is firmly attached to the underlying vocal ligaments. It is loosely adherent to the anterior surface of the epiglottis, but firmly attached to its anterior surface and the floor of the valleculae. On the aryepiglottic folds it is reinforced by a considerable amount of fibrous connective tissue, and it adheres closely to the laryngeal surfaces of the cuneiform and arytenoid cartilages.

The laryngeal epithelium is mainly a ciliated, pseudostratified respiratory epithelium where it covers the inner aspects of the larynx, including the posterior, laryngeal surface of the epiglottis, and it provides a mucociliary clearance mechanism shared with most of the respiratory tract (see Ch. 57). However, the vocal folds are covered by non-keratinized, stratified squamous epithelium where they contact each other: this important variation protects the tissue from the effects of the considerable mechanical stresses that act on the surfaces of the vocal folds. The exterior surfaces of the larynx, which merge with the laryngopharynx and oropharynx (including the anterior, lingual surface of the epiglottis and the aryepiglottic folds), are subject to the abrasive effects of swallowed food, and are therefore covered by non-keratinized, stratified squamous epithelium.

The laryngeal mucosa has numerous mucous glands, especially over the epiglottis, where they pit the cartilage, and along the margins of the aryepiglottic folds anterior to the arytenoid cartilages, where they are known as the arytenoid glands. Many large glands in the saccules of the larynx secrete periodically over the vocal folds during phonation. The free edges of these folds are devoid of glands, and their stratified epithelium is vulnerable to drying and requires the secretions of neighbouring glands: hoarseness as a result of excessive speaking is due to partial temporary failure of this secretion. The epithelial surfaces are ridged and this may help retain the lubricating secretions over the surfaces of the edges of the folds. Poorly lubricated folds offer increased resistance to airflow, which means that higher subglottal pressures are needed to initiate phonation. Taste buds, like those in the tongue, occur on the posterior epiglottic surface, aryepiglottic folds and less often in other laryngeal regions.

UPPER PART

The upper part of the laryngeal cavity contains the laryngeal inlet (aditus), the aryepiglottic fold and the laryngeal vestibule (introitus).

Laryngeal inlet (aditus)

The upper part of the laryngeal cavity is entered by the laryngeal inlet (aditus laryngis), the aperture between the larynx and pharynx. This faces backwards and somewhat upwards, because the anterior wall of the larynx is much longer than the posterior (and slopes downwards and forwards in its upper part because of the oblique inclination of the epiglottis). The inlet is bounded anteriorly by the upper edge of the epiglottis, posteriorly by the transverse mucosal fold between the two arytenoids (posterior commissure), and on each side by the edge of a mucosal ridge, the aryepiglottic fold, that runs between the side of the epiglottis and the apex of the arytenoid cartilage. The midline groove between the two corniculate tubercles is termed the interarytenoid notch.

Aryepiglottic fold

The aryepiglottic fold contains ligamentous and muscular fibres. The ligamentous fibres represent the free upper border of the quadrangular membrane (Fig. 34.5). The muscle fibres are continuations of the oblique arytenoids. The posterior part of the aryepiglottic fold contains two oval swellings, one above and in front, the other behind and below, that mark the positions of the underlying cuneiform and corniculate cartilages respectively. They are separated by a shallow vertical furrow which is continuous below with the opening of the laryngeal ventricle.

Laryngeal vestibule (introitus)

Vestibule is a clinical term that denotes the space between the laryngeal inlet and vestibular folds. It is wide above, narrow below, and higher anteriorly than posteriorly. Its anterior wall is formed by the posterior surface of the epiglottis, the lower part of which (epiglottic tubercle) bulges backwards a little. Its lateral walls, which are higher in front and shallow behind, are formed by the medial surfaces of the aryepiglottic folds. Its posterior wall consists of the interarytenoid mucosa above the ventricular folds.

MIDDLE PART

The middle part of the laryngeal cavity is the smallest, and extends from the rima vestibuli above to the rima glottidis below. On each side it contains the vestibular folds, the ventricle and the saccule of the larynx.

Vestibular folds and ligaments

The narrow vestibular ligament represents the thickened lower border of the quadrangular membrane (Fig. 34.5). It is fixed in front to the thyroid angle below the epiglottic cartilage and behind to the anterolateral surface of the arytenoid cartilage above its vocal process. With its covering of mucosa, it is termed the vestibular (ventricular or false vocal) fold (Figs 34.5, 34.6). The presence of a loose vascular mucosa lends the vestibular folds a pink appearance in vivo, as they lie above and lateral to the vocal cords.

Ventricle (sinus) of the larynx

The laryngeal ventricle is a slit between the vestibular and vocal cords (Figs 34.5, 34.6). It opens into a fusiform recess on each side of the larynx and extends upwards into the laryngeal wall lateral to the vestibular fold, opening into the saccule.