There is another pair of mucosal recesses (piriform fossae) between the central part of the larynx and the more lateral lamina of the thyroid cartilage. The piriform fossae form channels that direct solids and liquids from the oral cavity around the raised laryngeal inlet and into the esophagus.
Collections of lymphoid tissue in the mucosa of the pharynx surrounding the openings of the nasal and oral cavities (Waldeyer’s tonsillar ring) are part of the body’s defense system. The largest of these collections form distinct masses (tonsils). Tonsils occur mainly in three areas (Fig. 8.205):
The pharyngeal tonsil, known as adenoids when enlarged, is in the midline on the roof of the nasopharynx.
The palatine tonsils are on each side of the oropharynx between the palatoglossal and palatopharyngeal arches just posterior to the oropharyngeal isthmus. (The palatine tonsils are visible through the open mouth of a patient when the tongue is depressed.)
The lingual tonsils refer collectively to numerous lymphoid nodules on the posterior one-third of the tongue.
Small lymphoid nodules also occur in the pharyngotympanic tube near its opening into the nasopharynx, and on the upper surface of the soft palate.
Numerous vessels supply the pharyngeal wall (Fig. 8.206).
Arteries that supply upper parts of the pharynx include: the ascending pharyngeal artery, the ascending palatine and tonsillar branches of the facial artery, and numerous branches of the maxillary and the lingual arteries.
All these vessels are from the external carotid artery.
Arteries that supply the lower parts of the pharynx include pharyngeal branches from the inferior thyroid artery, which originates from the thyrocervical trunk of the subclavian artery.
The major blood supply to the palatine tonsil is from the tonsillar branch of the facial artery, which penetrates the superior constrictor muscle.
Veins of the pharynx form a plexus, which drains superiorly into the pterygoid plexus in the infratemporal fossa, and inferiorly into the facial and internal jugular veins (Fig. 8.207).
Lymphatic vessels from the pharynx drain into the deep cervical nodes and include retropharyngeal (between the nasopharynx and vertebral column), paratracheal, and infrahyoid nodes (Fig. 8.207).
The palatine tonsils drain through the pharyngeal wall into the jugulodigastric nodes in the region where the facial vein drains into the internal jugular vein (and inferior to the posterior belly of the digastric muscle).
Motor and most sensory innervation (except for the nasal region) of the pharynx is mainly through branches of the vagus [X] and glossopharyngeal [IX] nerves, which form a plexus in the outer fascia of the pharyngeal wall (Fig. 8.208A).
The pharyngeal plexus is formed by: the pharyngeal branch of the vagus nerve [X], branches from the external laryngeal nerve from the superior laryngeal branch of the vagus nerve [X], and pharyngeal branches of the glossopharyngeal nerve [IX].
The pharyngeal branch of the vagus nerve [X] originates from the upper part of its inferior ganglion above the origin of the superior laryngeal nerve and is the major motor nerve of the pharynx.
All muscles of the pharynx are innervated by the vagus nerve [X] mainly through the pharyngeal plexus, except for the stylopharyngeus, which is innervated directly by a branch of the glossopharyngeal nerve [IX] (Fig. 8.208B).