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The Pharynx


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The Pharynx
The pharynx is that part of the digestive tube which is placed behind the nasal cavities, mouth, and larynx. It is a musculomembranous tube, somewhat conical in form, with the base upward, and the apex downward, extending from the under surface of the skull to the level of the cricoid cartilage in front, and that of the sixth cervical vertebra behind.   1
  The cavity of the pharynx is about 12.5 cm. long, and broader in the transverse than in the antero-posterior diameter. Its greatest breadth is immediately below the base of the skull, where it projects on either side, behind the pharyngeal ostium of the auditory tube, as the pharyngeal recess (fossa of Rosenmüller); its narrowest point is at its termination in the esophagus. It is limited, above, by the body of the sphenoid and basilar part of the occipital bone; below, it is continuous with the esophagus; posteriorly, it is connected by loose areolar tissue with the cervical portion of the vertebral column, and the prevertebral fascia covering the Longus colli and Longus capitis muscles; anteriorly, it is incomplete, and is attached in succession to the medial pterygoid plate, pterygomandibular raphé, mandible, tongue, hyoid bone, and thyroid and cricoid cartilages; laterally, it is connected to the styloid processes and their muscles, and is in contact with the common and internal carotid arteries, the internal jugular veins, the glossopharyngeal, vagus, and hypoglossal nerves, and the sympathetic trunks, and above with small parts of the Pterygoidei interni. Seven cavities communicate with it, viz., the two nasal cavities, the two tympanic cavities, the mouth, the larynx, and the esophagus. The cavity of the pharynx may be subdivided from above downward into three parts: nasal, oral, and laryngeal (Fig. 994).   2
  The Nasal Part of the Pharynx (pars nasalis pharyngis; nasopharynx) lies behind the nose and above the level of the soft palate: it differs from the oral and laryngeal parts of the pharynx in that its cavity always remains patent. In front (Fig. 1029) it communicates through the choanæ with the nasal cavities. On its lateral wall is the pharyngeal ostium of the auditory tube, somewhat triangular in shape, and bounded behind by a firm prominence, the torus or cushion, caused by the medial end of the cartilage of the tube which elevates the mucous membrane. A vertical fold of mucous membrane, the salpingopharyngeal fold, stretches from the lower part of the torus; it contains the Salpingopharyngeus muscle. A second and smaller fold, the salpingopalatine fold, stretches from the upper part of the torus to the palate. Behind the ostium of the auditory tube is a deep recess, the pharyngeal recess (fossa of Rosenmüller). On the posterior wall is a prominence, best marked in childhood, produced by a mass of lymphoid tissue, which is known as the pharyngeal tonsil. Above the pharyngeal tonsil, in the middle line, an irregular flask-shaped depression of the mucous membrane sometimes extends up as far as the basilar process of the occipital bone; it is known as the pharyngeal bursa.   3


FIG. 1029– Front of nasa part of pharynx, as seen with the laryngoscope. (See enlarged image)
 
  The Oral Part of the Pharynx (pars oralis pharyngis) reaches from the soft palate to the level of the hyoid bone. It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil.   4
  The Laryngeal Part of the Pharynx (pars laryngea pharyngis) reaches from the hyoid bone to the lower border of the cricoid cartilage, where it is continuous with the esophagus. In front it presents the triangular entrance of the larynx, the base of which is directed forward and is formed by the epiglottis, while its lateral boundaries are constituted by the aryepiglottic folds. On either side of the laryngeal orifice is a recess, termed the sinus piriformis, which is bounded medially by the aryepiglottic fold, laterally by the thyroid cartilage and hyothyroid membrane.   5
 
Muscles of the Pharynx.—The muscles of the pharynx (Fig. 1030) are:   6
Constrictor inferior.
Stylopharyngeus.
Constrictor medius.
Salpingopharyngeus.
Constrictor superior.
Pharyngopalatinus. 162
  The Constrictor pharyngis inferior (Inferior constrictor) (Figs. 1030, 1031), the thickest of the three constrictors, arises from the sides of the cricoid and thyroid cartilage. From the cricoid cartilage it arises in the interval between the Cricothyreoideus in front, and the articular facet for the inferior cornu of the thyroid cartilage behind. On the thyroid cartilage it arises from the oblique line on the side of the lamina, from the surface behind this nearly as far as the posterior border and from the inferior cornu. From these origins the fibers spread backward and medialward to be inserted with the muscle of the opposite side into the fibrous raphé in the posterior median line of the pharynx. The inferior fibers are horizontal and continuous with the circular fibers of the esophagus; the rest ascend, increasing in obliquity, and overlap the Constrictor medius.   7
  The Constrictor pharyngis medius (Middle constrictor) (Figs. 1030, 1031) is a fanshaped muscle, smaller than the preceding. It arises from the whole length of the upper border of the greater cornu of the hyoid bone, from the lesser cornu, and from the stylohyoid ligament. The fibers diverge from their origin: the lower ones descend beneath the Constrictor inferior, the middle fibers pass transversely, and the upper fibers ascend and overlap the Constrictor superior. It is inserted into the posterior median fibrous raphé, blending in the middle line with the muscle of the opposite side.   8


FIG. 1030– Muscles of the pharynx and cheek. (See enlarged image)
 
  The Constrictor pharyngis superior (Superior constrictor) (Fig. 1030, 1031) is a quadrilateral muscle, thinner and paler than the other two. It arises from the lower third of the posterior margin of the medial pterygoid plate and its hamulus, from the pterygomandibular raphé, from the alveolar process of the mandible above the posterior end of the mylohyoid line, and by a few fibers from the side of the tongue. The fibers curve backward to be inserted into the median raphé, being also prolonged by means of an aponeurosis to the pharyngeal spine on the basilar part of the occipital bone. The superior fibers arch beneath the Levator veli palatini and the auditory tube. The interval between the upper border of the muscle and the base of the skull is closed by the pharyngeal aponeurosis, and is known as the sinus of Morgagni.   9
  The Stylopharyngeus (Fig. 1019) is a long, slender muscle, cylindrical above, flattened below. It arises from the medial side of the base of the styloid process, passes downward along the side of the pharynx between the Constrictores superior and medius, and spreads out beneath the mucous membrane. Some of its fibers are lost in the Constrictor muscles, while others, joining with the Pharyngopalatinus, are inserted into the posterior border of the thyroid cartilage. The glossopharyngeal nerve runs on the lateral side of this muscle, and crosses over it to reach the tongue.   10
  The Salpingopharyngeus (Fig. 1028) arises from the inferior part of the auditory tube near its orifice; it passes downward and blends with the posterior fasciculus of the Pharyngopalatinus.   11
 
Nerves.—The Constrictores and Salpingopharyngeus are supplied by branches from the pharyngeal plexus, the Constrictor inferior by additional branches from the external laryngeal and recurrent nerves, and the Stylopharyngeus by the glossopharyngeal nerve.   12
 
Actions.—When deglutition is about to be performed, the pharynx is drawn upward and dilated in different directions, to receive the food propelled into it from the mouth. The Stylopharyngei, which are much farther removed from one another at their origin than at their insertion, draw the sides of the pharynx upward and lateralward, and so increase its transverse diameter; its breadth in the antero-posterior direction is increased by the larynx and tongue being carried forward in their ascent. As soon as the bolus of food is received in the pharynx, the elevator muscles relax, the pharynx descends, and the Constrictores contract upon the bolus, and convey it downward into the esophagus.   13
 
Structure.—The pharynx is composed of three coats: mucous, fibrous, and muscular.   14
  The pharyngeal aponeurosis, or fibrous coat, is situated between the mucous and muscular layers. It is thick above where the muscular fibers are wanting, and is firmly connected to the basilar portion of the occipital and the petrous portions of the temporal bones. As it descends it diminishes in thickness, and is gradually lost. It is strengthened posteriorly by a strong fibrous band, which is attached above to the pharyngeal spine on the under surface of the basilar portion of the occipital bone, and passes downward, forming a median raphé, which gives attachment to the Constrictores pharyngis.   15
  The mucous coat is continuous with that lining the auditory tubes, the nasal cavities, the mouth, and the larynx. In the nasal part of the pharynx it is covered by columnar ciliated epithelium; in the oral and laryngeal portions the epithelium is stratified squamous. Beneath the mucous membrane are found racemose mucous glands; they are especially numerous at the upper part of the pharynx around the orifices of the auditory tubes.   16


FIG. 1031– Muscles of the pharynx, viewed from behind, together with the associated vessels and nerves. (Modified after Testut.) (See enlarged image)
 



Note 162.  The Pharyngopalatinus is described with the muscles of the palate (p. 1139). [back]