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Chapter 53: The pharynx and larynx

Pharynx

The word throat is used for the parts of the neck anterior to the vertebral column, especially the pharynx and the larynx. The pharynx is the part of the digestive system situated posterior to the nasal and oral cavities and posterior to the larynx. It is therefore divisible into nasal, oral, and laryngeal parts: the (1) nasopharynx, (2) oropharynx, and (3) laryngopharynx. The pharynx extends from the base of the skull down to the inferior border of the cricoid cartilage (around the C6 vertebral level), where it becomes continuous with the esophagus. Its superior aspect is related to the sphenoid and occipital bones and the posterior aspect to the prevertebral fascia and muscles as well as the upper six cervical vertebrae. The pharynx (figs. 53-1, 53-2, 53-3 and 53-4) is a fibromuscular tube lined by mucous membrane.

The pharynx is the common channel for deglutition (swallowing) and respiration, and the food and air pathways cross each other in the pharynx. In the anesthetized patient, the passage of air through the pharynx is facilitated by extension of the neck.

Subdivisions

Nasopharynx.

The nasopharynx, at least in its anterior part, may be regarded as the posterior portion of the nasal cavity, with which it has a common function as part of the respiratory system. The nasopharynx communicates with the oropharynx through the pharyngeal isthmus, which is bounded by the soft palate, the palatopharyngeal arches, and the posterior wall of the pharynx. The isthmus is closed by muscular action during swallowing. The choanae are the junction between nasopharynx and the nasal cavity proper.

A mass of lymphoid tissue, the (naso)pharyngeal tonsil is embedded in the mucous membrane of the posterior wall of the nasopharynx. Enlarged (naso)pharyngeal tonsils are termed "adenoids" and may cause respiratory obstruction. Higher up, a minute pharyngeal hypophysis (resembling the adenohypophysis) may be found (see fig. 53-5).

Each lateral wall of the nasopharynx has the pharyngeal opening of the auditory tube, located about 1 to 1.5 cm (1) inferior to the roof of the pharynx, (2) anterior to the posterior wall of the pharynx, (3) superior to the level of the palate, and (4) posterior to the inferior nasal concha and the nasal septum (fig. 53-5). The auditory tube can be catheterized through a nostril. The opening is limited on the superior side by a tubal elevation (tubal torus), from which mucosal folds descend to the palate and side wall of the pharynx. The part of the pharyngeal cavity posterior to the tubal elevation is termed the pharyngeal recess. Nearby lymphoid tissue is referred to as the tubal tonsil.

The auditory tube is pharyngotympanic; i.e., it connects the nasopharynx to the tympanic cavity. Hence, infections may spread along this route. The tube equalizes the pressure of the external air and that in the tympanic cavity. The auditory tube, about 3 to 4 cm in length, extends posteriorly, laterally, and superiorly. It consists of (1) a cartilaginous part, the anteromedial two thirds, which is a diverticulum of the pharynx, and (2) an osseous part, the posterolateral third, which is an anteromedial prolongation of the tympanic cavity. The cartilaginous part lies on the inferior aspect of the skull, in a groove between the greater wing of the sphenoid bone and the petrous part of the temporal bone (see fig. 42-12). The cartilaginous part of the auditory tube remains closed except on swallowing or yawning, when its opening prevents excessive pressure in the middle ear. The osseous part of the tube is within the petrous part of the temporal bone.

Oropharynx.

The oropharynx extends inferiorward from the soft palate to the superior border of the epiglottis. It communicates anteriorly with the oral cavity by the faucial (oropharyngeal) isthmus, which is bounded superiorly by the soft palate, laterally by the palatoglossal arches, and inferiorly by the tongue (see fig. 53-1). This area is characterized by a lymphatic ring composed of the nasopharyngeal, tubal, palatine, and lingual tonsils.

The mucous membrane of the epiglottis is reflected onto the base of the tongue and onto the lateral wall of the pharynx. The space on each side of the median glosso-epiglottic fold is termed the epiglottic vallecula.

Each lateral wall of the oropharynx has the diverging palatoglossal and palatopharyngeal arches, which are produced by the similarly named muscles and are often called the anterior and posterior pillars of the fauces, respectively. The triangular recess (tonsillar fossa) between the two arches lodges the palatine tonsil, which is often referred to as merely "the tonsil" (see fig. 53-1). (A tonsil is a mass of lympoid tissue containing reaction or germinal centers and related to an epithelial surface in the pharynx.) The medial surface of the tonsil usually has an intratonsillar cleft (commonly but inaccurately called the "supratonsillar fossa") and a number of crypts (fig. 53-6). The lateral surface is covered by a fibrous capsule and is related to fascia, the paratonsillar vein (the chief source of hemorrhage after tonsillectomy), and pharyngeal musculature. The tonsil is supplied by the tonsillar branch of the facial artery, and it drains into the facial vein. Involution of the tonsil begins at puberty.

Laryngopharynx.

The laryngopharynx extends from the superior border of the epiglottis to the inferior border of the cricoid cartilage, where it becomes continuous with the esophagus. Its anterior aspect has the inlet of the larynx and the posterior aspects of the arytenoid and cricoid cartilages. The piriform recess, in which foreign bodies may become lodged, is the part of the cavity of the laryngopharynx situated on each side of the inlet of the larynx (see fig. 53-3).

Muscles

The pharynx consists of four coats of muscles, from within outward: (1) a mucous membrane continuous with that of the auditory tubes and the nasal, oral, and laryngeal cavities; (2) a fibrous coat, that is thickest in its superior extent (pharyngobasilar fascia) and that forms a median raphe posteriorly; (3) a muscular coat, described below; and (4) a fascial coat (buccopharyngeal fascia) covering the outer surface of the muscles.

The wall of the pharynx is composed mainly of two layers of skeletal muscles. The external, circular layer comprises three constrictors (fig. 53-7 and table 53-1). The internal, chiefly longitudinal layer consists of two levators: the stylopharyngeus and the palatopharyngeus.

The constrictors of the pharynx have their fixed points in the anterior larynx, where they are attached to bones or cartilages, whereas they expand posteriorly, overlap one another from inferior to superior, and end in a median tendinous raphe in the posterior midline. Their overlapping has been compared with that of three flower pots placed one inside another. The inferior constrictor arises from the cricoid and thyroid cartilages. The cricopharyngeal fibers are horizontal in orientation and continuous with the circular fibers of the esophagus. These fibers act as a sphincter and prevent air from entering the esophagus. A pharyngeal diverticulum may form posterior to the larynx through the fibers of the inferior constrictor. The middle constrictor arises from the hyoid bone, whereas the superior constrictor arises from the mandible and sphenoid bone. * The constrictor muscles are inserted into the median raphe posteriorly.

The palatopharyngeus muscle arises from the palate, forms the palatopharyngeal fold, and is inserted into the thyroid cartilage and the side of the pharynx. The stylopharyngeus muscle arises from the styloid process, passes between the superior and middle constrictors, and is inserted with the palatopharyngeus. The stylopharyngeus is supplied by the glossopharyngeal nerve, whereas the palatopharyngeus and the constrictor muscles are innervated by the pharyngeal branch of the vagus nerve (probably fibers from the accessory nerve) through the pharyngeal plexus that is located on the middle constrictor.

The chief action in which the muscles of the pharynx combine is deglutition (or swallowing), a complicated, neuromuscular act whereby food is transferred from (1) the mouth through (2) the pharynx and (3) the esophagus to the stomach. The pharyngeal stage is the most rapid and most complex phase of deglutition. During swallowing, the nasopharynx and vestibule of the larynx are sealed but the epiglottis adopts a variable position. Food is usually deviated laterally by the epiglottis and ary-epiglottic folds into the piriform recesses of the laryngopharynx, lateral to the larynx. The pharyngeal ridge is an elevation or bar on the posterior wall of the pharynx inferior to the level of the soft palate; it is produced during swallowing by transverse muscle fibers.

Innervation and blood supply

The motor and most of the sensory supply to the pharynx is by way of the pharyngeal plexus, which, situated chiefly on the middle constrictor, is formed by the pharyngeal branches of the vagus and glossopharyngeal nerves and also by sympathetic nerve fibers. The motor fibers in the plexus are carried by the vagus (although they likely represent cranial accessory nerve components) and supply all the muscles of the pharynx and soft palate except the stylopharyngeus (supplied by cranial nerve IX) and tensor veli palatini (supplied by cranial nerve V). The sensory fibers in the plexus are from the glossopharyngeal nerve, and they supply the greater portion of all three parts of the pharynx. The pharynx is supplied by branches of the external carotid (ascending pharyngeal) and subclavian (inferior thyroid) arteries.

Larynx

The larynx is the organ that connects the lower part of the pharynx with the trachea. It serves (1) as a valve to guard the air passages, especially during swallowing, (2) for the maintenance of a patent airway, and (3) for vocalization.

The anterior aspect of the larynx is quite superficial (fig. 53-8) and the posterior aspect of the larynx is related to the laryngopharynx, the prevertebral fascia and muscles, and to the bodies of cervical vertebrae 3 to 6. Laterally, the larynx is related to the carotid sheath, infrahyoid muscles, sternomastoid muscle, and the thyroid gland. The larynx is elevated (particularly by the palatopharyngeus muscle) during extension of the head and during deglutition.

The larynx can be examined in vivo by means of a mirror (indirect laryngoscopy) or a fiber optic instrument (direct laryngoscopy) (see figs. 53-11C and D and 53-12).

Cartilages (figs. 53-8, 53-9, 53-10 and 53-14)

The larynx possesses three single cartilages (thyroid, cricoid, and epiglottic) and three paired cartilages (arytenoid, corniculate, and cuneiform). The thyroid, cricoid, and arytenoid cartilages are composed of hyaline cartilage and may undergo calcification, endochondral ossification, or both, thereby becoming visible radiographically. The other cartilages are elastic in type.

The thyroid cartilage (fig. 53-9) comprises two spring-like plates termed laminae, which are fused anteriorly but divergent posteriorly. The laminae produce a median elevation termed the laryngeal prominence ("Adam's apple"), which is palpable and frequently visible. The posterior border of each lamina is prolonged superiorly and inferiorly as cornua, or horns. The superior horn is anchored to the tip of the greater horn of the hyoid bone. The inferior horn articulates medially with the cricoid cartilage. The lateral surface of each lamina is crossed by an oblique line for the attachment of muscles.

The cricoid cartilage (fig. 53-9) is shaped like a signet ring. It comprises a posterior plate, called the lamina, and a narrow, anterior part, the arch. The lamina articulates superolaterally with the arytenoid cartilages. The cricoid cartilage is at the level of the C6 vertebra, and its arch is palpable. The inferior border of the cricoid cartilage marks the end of the pharynx and larynx and hence the commencement of the esophagus and trachea.

The arytenoid cartilages (fig. 53-9B) articulate with the superior border of the lamina of the cricoid cartilage. Each has a superiorly-positioned apex (which supports the corniculate cartilage) and a base that comprises its inferior part. The base sends a vocal process anteriorward (for attachment to the vocal ligament) and a lateral, muscular process (for muscular attachments). The corniculate and (inconstant) cuneiform cartilages are nodules in the aryepiglottic folds (figs. 53-10B and 53-12).

The epiglottic cartilage (see fig. 53-9) is covered by mucous membrane to form the epiglottis. The epiglottis is situated posterior to the root of the tongue and the body of the hyoid bone and anterior to the inlet of the larynx. The inferior end, or stalk, of the leaf-shaped cartilage is anchored to the posterior aspect of the thyroid cartilage. Taste buds are present in the posterior surface of the epiglottis.

Joints (fig. 53-9)

Two synovial joints are present on each side. The cricothyroid joint, between the lateral aspect of the cricoid cartilage and the inferior horn of the thyroid cartilage, allows mainly rotation of the thyroid cartilage around a horizontal axis through the joints of the two sides. This produces a tipping motion where the anterior part of the thyroid cartilage moves anterior and inferior. The cricoarytenoid joint, between the superior border of the lamina of the cricoid cartilage and the base of the arytenoid cartilages, allows gliding and rotation of the arytenoid cartilages.

Ligaments

The thyrohyoid membrane connects the thyroid cartilage with the superior border of the hyoid bone (see fig. 53-9C). The median part is thickened to form a ligament. The membrane is pierced on each side by the internal laryngeal nerve and the superior laryngeal vessels.

The cricothyroid ligament (see fig. 53-8) connects the arch of the cricoid cartilage with the thyroid cartilage. The term conus elasticus (fig. 53-10A) is used for elastic fibers that extend superiorward from the cricoid cartilage to the vocal ligaments (cricovocal membrane). In acute respiratory obstruction, cricothyrotomy, that is, entering the larynx between the arch of the cricoid cartilage and the thyroid cartilage by penetrating the cricothyroid membrane, is preferable to tracheotomy for the non-surgeon.

The vocal ligament on each side extends posteriorward from its anterior attachment on the thyroid cartilage to a  posterior attachment on the vocal process of the arytenoid cartilage. This "vocal cord" is the upper border of the conus elasticus. The vocal cords are composed of elastic fibers covered tightly by a vocal fold of mucous membrane (fig. 53-10B). The vestibular ligament on each side is an indefinite band situated superior to the vocal ligament and covered loosely by the vestibular fold.

The epiglottis is attached by ligaments to the hyoid bone, to the posterior aspect of the tongue, to the sides of the pharynx, and to the thyroid cartilage.

Inlet

The inlet, or aditus, of the larynx is the passageway from the laryngopharynx into the cavity of the larynx. It is set obliquely, facing largely posteriorward. It is bounded anteriorly by the superior border of the epiglottis, on each side by the aryepiglottic folds, and inferiorly and posteriorly by an interarytenoid fold (fig. 53-11C). The inlet is related laterally to the piriform recesses of the laryngopharynx (see fig. 53-3). The aryepiglottic folds provide lateral food channels that lead along the sides of the epiglottis, through the piriform recesses, and to the esophagus (fig. 53-12). Closure of the inlet protects the respiratory passages against the invasion of food and foreign bodies. This closure is produced by contraction of the aryepiglottic and transverse arytenoid muscles and by the posterior motion of the epiglottis that is produced by the elevation of the larynx. This elevation raises the base of the epiglottis more than the superior portions, resulting in a posterior tilting of the epiglottis.

Cavity

The cavity of the larynx is divided into three portions: (1) the vestibule; (2) the ventricles and the area between them; (3) and the infraglottic cavity. These regions are defined by the location of horizontal folds - the vestibular and the vocal folds (see fig. 53-10).

(1) The vestibule extends from the inlet to the vestibular folds.

(2) The ventricle extends laterally in the interval between the vestibular and vocal folds. Each ventricle resembles a canoe laid on its side, and the two ventricles communicate with one another through the median portion of the laryngeal cavity. A small diverticulum, the saccule, which extends superiorward from the anterior aspect of each ventricle, possesses mixed glands and has been termed the "oil can" of the vocal folds. The vestibular folds (see fig. 53-10A and B), or "false vocal cords," contain the vestibular ligaments and are protective rather than vocal in function. The vocal folds, or "vocal cords," which contain the vocal ligaments, are musculomembranous shelves that appear inferior and medial to the vestibular folds. They extend from the angle of the thyroid cartilage in the anterior larynx to its posterior attachment on the vocal processes of the arytenoid cartilages. The bulk of each vocal fold is formed by the vocalis muscle, which is a part of the thyro-arytenoid muscle. The vocal folds and processes, together with the interval (rima glottidis) between them, are collectively termed the glottis. The rima glottidis is the narrowest part of the laryngeal cavity and can be seen between the more separated vestibular folds during laryngoscopy (see fig. 53-11D). The mucous membrane over each vocal ligament has nonkeratinizing, stratified squamous epithelium, is firmly bound down, and appears white. The vocal folds control the stream of air passing through the rima and hence are important in voice production. The anterior, intermembranous part of the rima lies between the vocal folds, whereas the posterior, intercartilaginous part is situated between the arytenoid cartilages (see fig. 53-14). The shape and size of the rima are altered by movements of the arytenoid cartilages. The rima is wider during inspiration and quiet breathing and narrower during expiration and phonation. In surface anatomy, the rima glottidis is approximately on the level of the midpoint of the anterior margin of the thyroid cartilage.

(3) The infraglottic cavity extends from the rima glottidis to the trachea.

Closure

Three levels or tiers in the larynx can be closed by sphincteric muscles: (1) the inlet, which is closed during deglutition and protects the respiratory passages against the invasion of food; (2) the vestibular folds, closure of which traps  air in the trachea and makes possible an increase of intrathoracic pressure (as in coughing) or intra-abdominal pressure (as in micturition and defecation); and (3) the vocal folds, which are approximated in phonation. The presence of a foreign body is the commonest cause of laryngeal spasm, which usually involves not only the glottis but all of the sphincteric musculature of the larynx.

Mucous membrane

The mucosa of the larynx, which is continuous with that of the laryngopharynx and trachea, is loose except over the posterior part of the epiglottis and over the vocal ligaments. Hence this membrane may become raised abnormally by submucous fluid, as in edema of the larynx. The edema does not spread inferior to the level of the vocal folds, since it is limited by the tight attachment of the mucosa to the vocal ligaments.

Sensory innervation and blood supply

The mucosa of the larynx is supplied on each side chiefly by the internal laryngeal branch of the superior laryngeal nerve, which supplies the larynx as far down as the vocal folds. The inferior part of the larynx receives sensory fibers from the recurrent laryngeal nerve.

The larynx has arterial supply by (1) the superior laryngeal artery (from the superior thyroid), which accompanies the internal laryngeal nerve, and (2) the inferior laryngeal artery (from the inferior thyroid), which accompanies the recurrent laryngeal nerve.

Muscles of larynx

The larynx as a whole can be elevated and depressed by extrinsic muscles (e.g., the stylopharyngeus and palatopharyngeus and the infrahyoid muscles).

The intrinsic laryngeal muscles are complicated, but they may be classified as follows:

1. The sphincters of the inlet: transverse arytenoid; oblique arytenoid and aryepiglottic.

2. The muscles that close and open the rima glottidis: lateral cricoarytenoid (adductor) and posterior cricoarytenoid (abductor).

3. The muscles that regulate the vocal ligaments: thyroartenoid and vocalis; cricothyroid.

The muscles of the larynx are illustrated in figures 53-13 and 53-14D and summarized in table 53-2.

Three muscles arise from the cricoid cartilage: the cricothyroid, arising from the lateral aspect of the cricoid cartilage and passing posteriorward to insert on the lamina and inferior horn of the thyroid cartilage; the lateral cricoarytenoid, extending posteriorward to the muscular process of the arytenoid cartilage; and the posterior cricoarytenoid, extending laterally to the muscular process of the arytenoid cartiage (fig. 53-13). Two muscles, closely related to each other, connect the thyroid and arytenoid cartilages: the thyroarytenoid and the vocalis (fig. 53-14D). Two muscles unite the arytenoid cartilages: the transverse and oblique arytenoids (fig. 53-13D).

Abduction of the vocal cords is carried out solely by the posterior crico-arytenoid muscles, which, extending laterally from the posterior aspect of the cricoid cartilage to the muscular processes, rotate the arytenoid cartilages laterally (fig. 53-14B and C).  Abduction widens the gap of the glottis (batween the vocal cords), which is necessary for respiration. Adduction of the vocal cords is carried out by the lateral cricoarytenoid muscles, which, extending posteriorward from the arch of the cricoid cartilage to the muscular processes, rotate the arytenoid cartilages medially (fig. 53-14D). This closes  the glottis, as in phonation (fig. 53-14A, B and C). The oblique and transverse arytenoid muscles are needed in order to maintain approximation of the posterior portions of the vocal cords. After closure of the glottis, the vocal folds can be tightened and lengthened by the cricothyroid muscles to change the pitch and tone of the voice. The cricothyroid muscle, by tipping the thyroid cartilage anterior on the cricoid cartilage will increase the anteroposterior dimension of the larynx and tighten the vocal cord.

Motor innervation

All of the intrinsic muscles, with the exception of the cricothyroid, are supplied by the recurrent laryngeal nerve from the vagus. The cricothyroid is supplied by the external laryngeal branch of the superior laryngeal nerve from the vagus. The motor nerve fibers of the various laryngeal muscles are believed to originate from the brain as a cranial part of the accessory nerve before joining the vagus prior to leaving the skull. Unilateral damage of a recurrent laryngeal nerve results in paralysis of all the intrinsic muscles of the larynx except the cricothyroid, which will tend to adduct the vocal cord.

Additional reading

Jackson, C., and Jackson, C. L., Diseases of the Nose, Throat, and Ear, 2nd ed., W. B. Saunders Company, Philadelphia, 1959. This classic text contains an interesting chapter on laryngeal paralyses.

Tucker, G. F., Human Larynx. Coronal Section Atlas, Armed Forces Institute of Pathology, Washington, D.C., 1971. Black-and-white photomicrographs with labels.

Questions

53-1 Anterior to which vertebrae is the pharynx situated?

53-1 The pharynx is situated anterior to cervical vertebra 1 to 6 (see fig. 53-1). Occasionally the nasopharynx and laryngopharynx are referred to as the epipharynx and hypopharynx, respectively. Similarly, the epitympanic recess and the tympanic cavity inferior to the level of the tympanic membrane are sometimes called the epitympanum and hypotympanum, respectively.

53-2 What is the nasopharynx?

53-2 The nasopharynx is the superiormost part of the pharynx, but (at least in its anterior aspect) it may also be regarded as the posterior portion of the nasal cavity (F. W. Jones, J. Anat., 74:147,1940; K. Leela, R. Kanagasuntheram, and F. Y. Khoo, J. Anat., 117:333, 1974).

53-3 What are the boundaries of the pharyngeal isthmus?

53-3 The pharyngeal isthmus (between the nasopharynx and oropharynx) is bounded by the soft palate, palatopharyngeal arches, and posterior wall of the pharynx.

53-4 What are adenoids?

53-4 Adenoids (Gk, gland-like) are hypertrophied (naso)pharyngeal tonsils on the posterior wall of the nasopharynx. They may cause respiratory obstruction. Their removal (adenoidectomy), which was first undertaken in 1868, is generally combined with tonsillectomy.

53-5 What is the pharyngeal hypophysis?

53-5 The pharyngeal hypophysis, situated on the posterior wall of the pharynx, develops at the pharyngeal end of the stalk of the craniopharyngeal pouch (Rathke, 1838). Like the sellar hypophysis, it is an endocrine gland (P. McGrath, J. Endocrinol., 42:205, 1968) and contains several types of secretory cells (C. B. Gonzalez, G. F. Valdes, and D. R. Ciocca, Acta Anat., 97:224, 1977).

53-6 Where are the openings of the auditory tube?

53-6 The so-called auditory tube, described by Eustachi (1563) but known even before the time of Christ, would be better named the pharyngotympanic tube. Its cartilaginous part is a diverticu1um of the pharynx that opens posterior to the inferior nasal concha (see fig. 53-4). The osseous part is a prolongation of the tympanic cavity opening from the anterior wall of the cavity. The tube is closed at rest but opens during swallowing and phonation, perhaps by a "milking" action of the levator and tensor (S. Seifand A. L. Dellon, Cleft Palate J., 15:329,1978; see also V. K. Misurya, Arch. Otolaryngol., 102: 265,1976). A detailed account of the tube is available in J. Terracol, A. Corone, and Y. Guerrier, La trompe d'Eustache,'Masson, Paris, 1949.

53-7 What are the boundaries of the faucial isthmus?

53-7 The faucial (or oropharyngeal) isthmus is bounded by the soft palate, palatoglossal arches, and tongue.

53-8 List the components of the pharyngeal lymphatic ring.

53-8 The pharyngeal lymphatic ring (Waldeyer, 1884) comprises the nasopharyngeal, tubal, palatine, and lingual tonsils. It is presumed to be a protective collar against infections and organisms that might enter through the nose and mouth.

53-9 Where is the tonsil?

53-9 The (palatine) tonsils are located between diverging pillars on each side of the pharynx, namely the palatoglossal and palatopharyngeal arches. Tonsillectomy, an operation described by Celsus in the first century A.D., is now performed either by dissection or by a special instrument known as a guillotine.

53-10 What is the piriform recess?

53-10 The piriform recess (or sinus or fossa), in which foreign bodies may become lodged, is the part of the cavity of the laryngopharynx situated on each side of the inlet of the larynx (see fig. 53-3).

53-11 Where does a pharyngeal diverticulum usually form?

53-11 A pharyngeal diverticulum usually forms posteriorly through the fibers of the inferior constrictor (between the thyropharyngeal and cricopharyngeal fibers). Increased intrapharyngeal pressure is regarded as an important factor in the production of a "pulsion diverticulum" through a weak area ("Killian's dehiscence") between the parts of the inferior constrictor. Moreover, swallowing in the presence of cricopharyngeal incoordination may be important in allowing mucosal herniation through a weak area in the pharyngeal wall (W. S. Payne and A. M. Olsen, The Esophagus, Lea & Febiger, Philadelpha, 1974). Regurgitation and difficulty in swallowing (dysphagia) may result, so that surgical excision may be indicated. Normally, a sphincteric zone is described immediately inferior to it, although also supplemented by, the inferior constrictor (C. Zaino et al., The Pharyngoesophageal Sphicter, Thomas, Springfield, Illinois, 1970).

53-12 What is the motor innervation of the pharynx?

53-12 The motor innervation of the pharynx is chiefly through the pharyngeal plexus, which is formed by the pharyngeal branches of cranial nerves X and IX. The vagus nerve provides most of the motor innervation. These motor fibers are derived from the accessory nerve. The glossopharyngeal nerve is mostly sensory.

53-13 How may the interior of the larynx be viewed in vivo?

53-13 The interior of the larynx may be viewed in vivo either indirectly through a laryngeal mirror or directly through a laryngoscope (see figs. 53-11C and D and 53-12). During the nineteenth century, the stethoscope, ophthalmoscope, laryngoscope, gastroscope, cystoscope, rectoscope, and bronchoscope were invented, in that order.

53-14 What is the vertebral level corresponding to the inferior extent of the larynx?

53-14 The larynx ends opposite the C6 vertebra, where the pharynx and larynx become continuous with the esophagus and trachea, respectively.

53-15 Is the hyoid bone a part of the larynx?

53-15 The hyoid bone is generally not included as a part of the larynx. The larynx is suspended from the hyoid bone, which is in turn suspended from the base of the skull. The styloid process, usually 30 mm in length, may be as long as 80 mm. The stylohyoid ligament, which connects it to the lesser horn of the hyoid bone, may become partly or even completely calcified, or it may become a chain of ossicles (J. R. Chandler, Laryngoscope, 87:1692, 1977).

53-16 Are the arytenoid cartilages fixed or mobile?

53-16 The arytenoid cartilages are extremely mobile. Arytenoid means shaped like a vase.

53-17 Where are the corniculate and cuneiform cartilages?

53-17 The corniculate cartilages (Santorini, 1724) are in the aryepiglottic folds and on the apices of the arytenoid cartilages, with which they form a posteriorward-projecting horn (or cornu; hence the name). The cuneiform cartilages (Wrisberg, 1786) are also in the aryepiglottic folds, immediately anterior to the corniculate. These cartilages form elevations that may be visible on laryngoscopy (see fig. 53-12). A small, unimportant nodule in the posterior border of the thyrohyoid membrane is known as the cartilago triticea (L., grain-like).

53-18 How may the larynx be entered in acute respiratory obstruction?

53-18 In acute respiratory obstruction, the infraglottic cavity may be entered through the cricothyroid ligament (cricothyrotomy).

53-19 Why have the vestibular folds been termed "false vocal cords"?

53-19 The vestibular folds are frequently referred to as "false vocal cords" because they do not produce voice sounds.

53-20 Which is the narrowest part of the laryngeal cavity?

53-20 The rima glottidis, i.e., the interval between the vocal folds, is the narrowest part of the laryngeal cavity.

53-21 What is the commonest cause of laryngeal spasm?

53-21 The presence of a foreign body is the commonest cause of laryngeal spasm.

53-22 Why does laryngeal edema not extend inferior to the glottis?

53-22 Mucosal swelling does not spread inferior to the glottis because the mucosa is closely adherent to the vocal folds.

53-23 What are the afferent fibers involved in the cough reflex?

53-23 Afferent vagal fibers from the larynx (superior laryngeal nerves), trachea, and bronchi reach the medulla. Then a deep inspiration is followed by closure of the vocal folds, forceful expiration, and sudden opening of the vocal folds. Foreign matter is usually removed by the rapidly moving air.

53-24 What are the results of injury (e.g., during thyroid surgery) to a recurrent laryngeal nerve?

53-24 Unilateral severance of a recurrent laryngeal nerve causes paralysis of the intrinsic muscles, except for the cricothyroid. However, the abductor (posterior cricoarytenoid) is usually affected first (Semon's rule), so that the involved vocal fold remains in the median plane, except when jostled by the normal fold (Chevalier Jackson). The voice is usually hoarse, as was shown experimentally in the dog by Galen in the second century.

Figure legends

Figure 53-1 General arrangement of the major parts of the pharynx as seen in a median section.

Figure 53-2 Scheme of respiratory and digestive cavities in the head and neck. Note that the pharynx acts as a common channel for both respiration and deglutition and that the air and food passages cross each other. (After Braus.)

Figure 53-3 Anterior wall of the pharynx viewed from the posterior aspect. The pharynx communicates with the nasal cavity, auditory tubes, oral cavity, larynx, and esophagus.

Figure 53-4 Sagittal (almost median) section of the head and neck, with a portion of the brain included. The various structures shown in this illustration have been given labels in other figures. Note the hypophysis, corpus callosum, septum pellucidum, pineal body, third ventricle, aqueduct, fourth ventricle, pons, cerebellum, medulla, and spinal cord; C1 to 7 vertebra as well as the T1 vertebra; the frontal and sphenoidal sinuses; the nasal conchae, palate, and opening of the auditory tube; the genioglossus and geniohyoid muscles; the larynx and trachea and pharynx and esophagus.

Figure 53-5  View of the right lateral wall of the nasopharynx from the medial side. See figure 53-4 for orientation.

Figure 53-6 A, Right palatine tonsil and its surroundings, medial aspect. B, Horizontal section through the tonsil, at a greater magnification. (After Fetterolf.)

Figure 53-7 Muscles of the pharynx. A, posterior aspect. B, right lateral aspect.

Figure 53-8 The structures in or near the anterior median line of the neck: (1) symphysis menti, (2) diaphragma oris (mylohyoid muscles) crossed by the digastric muscles, (3) hyoid bone, (4) median thyrohyoid ligament, (5) laryngeal prominence of the thyroid cartilage (overlying the glottis), (6) cricothyroid ligament, (7) arch of the cricoid cartilage, (8) cricotracheal ligament, (9) trachea and isthmus of the thyroid gland, (10) inferior thyroid veins forming a plexus, (11) jugular arch uniting the right and left jugular veins, (12) thymus (chiefly in childhood) and occasionally part of the brachiocephalic trunk or of the left brachiocephalic vein, and (13) jugular notch of the manubrium sterni. The infrahyoid muscles are not shown here.

Figure 53-9 The larynx. A, B, and C, Anterior, posterior, and right lateral views of cartilages. D, Right anterolateral aspect, showing the planes of section of figure 53-10. Note the thyroid and cricoid cartilages and the hyoid bone and epiglottic cartilage in A to D and the arytenoid cartilages in B.

Figure 53-10 A, Coronal and, B, median views of the larynx.

Figure 53-11 Ear, nose, and throat in vivo. A, The right tympanic membrane, showing the handle of the malleus. Cf. fig. 44-2. B, The nasopharynx and nasal cavities as seen in a mirror placed on the posterior pharyngeal wall. Note the posterior edge of the nasal septum, inferior nasal concha, and (on the right side of the illustration) the opening of the auditory tube. Cf. fig. 52-4. C, The larynx on inspiration, as seen in a mirror placed on the posterior pharyngeal wall. Note the epiglottis, ary-epiglottic folds, and (on the left side of the illustration) cuneiform cartilage, vestibular and vocal folds, and trachea. Cf. fig. 53-2. D, The larynx on phonation, as seen in a mirror. Note the vestibular and vocal folds: the latter are now approximated. (All photographs courtesy of Paul H. Holinger, M.D., Chicago, Illinois.)

Figure 53-12 Indirect laryngoscopy. A shows the placement of the mirror in the pharynx. B shows the structures seen during respiration. The upper part of the trachea can be seen through the open glottis. Cf. Fig. 53-11C.

Figure 53-13 Intrinsic muscles of the larynx. A and B, Right lateral aspect of the thyroid and cricoid cartilages. C, Medial aspect of the right half of the thyroid and cricoid cartilages. D, Posterior aspect of the arytenoid and cricoid cartilages.

Figure 53-14 The rima glottidis (in yellow) and the vocal ligaments in (A) phonation, (B) forced inspiration, and (C) quiet respiration. Note the rotation and lateral sliding of the arytenoid cartilages and the different shapes of the glottis. D, Muscles of the larynx seen from the superior aspect. The white arrows L and P show the direction of action of the lateral and posterior crico-arytenoid muscles, respectively. The black arrows show the direction of action of the transverse arytenoid muscle. M, muscular process of the arytenoid cartilage; V, vocal process of the arytenoid cartilage. It should be noticed that the apex of the A formed by the vocal ligaments is located anteriorly.

* The existence of a pterygomandibular raphe between the superior constrictor and buccinator has been denied by G. R. L. Gaughran (Anat. Rec., 184:410, 1976).

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