1130 DIGESTIVE SYSTEM 



External to the mucosa, there is a characteristic fibrous membrane, the pharyngeal apo- 

 neurosis [fascia pharyngobasilaris], which is well marked above, but below it loses its density 

 and gradually disappears as a definite structure. Above, it is attached to the basilar portion 

 of the occipital bone in front of the pharyngeal tubercle. Its attachment may be traced to 

 the apex of the petrous portion of the temporal bone, and thence to the auditory (Eustachian) 

 tube and medial lamina of the pterygoid process. It descends along the pterygo-mandibular 

 ligament to the posterior end of the mylohyoid ridge of the lower jaw, and passes thence along 

 the side of the tongue to the stylohyoid ligament, the hyoid bone, and thyreoid cartilage. 



External to the pharj^ngeal aponeurosis is a thick muscular layer, made up of various cross- 

 striated muscles, as wiU be described later. Outside of the muscular layer is a thin fibrous 

 tunica adventitia, connected with the adjacent prevertebral fascia by a loose, areolar tissue. 

 This loose tissue allows movement of the pharynx, and also favours the spreading of post- 

 pharjTigeal abscesses. 



The nasal pharynx (figs. 848, 888) belongs, strictly speaking, with the nasal 

 fossa as a part of the respiratory rather than the digestive system. Its anterior 

 wall is occupied by the two choance (posterior nares), with the nasal septum 

 between them. The floor is formed by the upper surface of the soft palate and in 

 a direct posterior continuation of the floor of the nasal fossae. Posteriorly, how- 

 ever, the floor presents a more or less narrowed opening, the pharyngeal isthmus, 

 which communicates with the oral pharynx below. The isthmus is formed ante- 

 riorly by the uvula, laterally by the posterior (pharyngo-palatine) arches. These 

 slope backward and downward to the posterior wall of the pharynx, which forms 

 the posterior boundary of the isthmus. The floor and isthmus change their form 

 and position greatly during the action of the palatal muscles, as will be mentioned 

 later. 



The lateral wall of the nasal pharynx presents above and behind, correspond- 

 ing to its widest point, a wide, slit-like lateral extension, the pharyngeal recess 

 [recessus pharyngeus] or fossa of Rosenmueller (fig. 888). Below and in front of 

 this recess, the greater part of the lateral wall is occupied by the aperture of the 

 auditory (Eustachian) tube [ostium pharyngeum tubse]. This is a somewhat 

 triangular, funnel-shaped opening, with an inconspicuous anterior lip [labium 

 anterius], a more distinct posterior lip [labium posterius], which presents poste- 

 riorly a rounded prominence (due to the projecting cartilage of the auditory tube), 

 called the torus tuharius. The prominence of the posterior lip facilitates the intro- 

 duction of the Eustachian catheter, in connection with which the location of the 

 aperture in the mid-lateral wall just above the level of the floor of the nasal fossa 

 should be carefully noted. On the lower aspect of the triangular aperture is a 

 slightly rounded fold, the levator cushion, which is a prominence caused by the 

 levator palati muscle. A fold of mucosa descending from the posterior lip of the 

 aperture to the lateral pharyngeal wall is the plica salpingo-pharyngea (due to 

 the m. salpingo-pharyngeus). An inconspicuous plica salpingo-palatina descends 

 from the anterior lip to the soft palate. 



The posterior wall (fig. 848) of the nasal pharynx slopes from below upward 

 and forward, passing (at the level of the anterior arch of the atlas) into the roof 

 [fornix pharyngis]. The roof is attached chiefly to the basi-occipital and basi- 

 sphenoid bones, extending laterally to the carotid canal of the pyramid, and ante- 

 riorly to the base of the nasal septum. In the posterior wall of the nasal pharynx 

 there is found in the mucosa a variable and inconstant blind sac, the pharyngeal 

 bursa. 



The mucosa of the roof, and to a certain extent also of the posterior wall, 

 especially in children, is thrown into numerous folds, which may be irregular or 

 radiate from the neighbourhood of the bursa. There is often a median longitu- 

 dinal groove (or sometimes ridge) at the posterior (inferior) end of which is the 

 bursa. These folds of the mucosa contain much lymphoid tissue, both diffuse 

 and in the form of numerous characteristic lymphoid nodules, with crypt-like 

 invaginations of the surface epithelium. This area constitutes the pharyngeal 

 tonsil [tonsilla pharyngea] (fig. 890), which is well-developed in children (often 

 abnormally enlarged, producing 'adenoids'), but usually, though not always, 

 atrophied in the adult. According to Symington, the involution of the pharyn- 

 geal tonsils begins at G or 7 years, and is usually completed at 10 years. In the 

 region of the pharyngeal tonsil and elsewhere, the mucosa presents numerous 

 small racemose mucous glands, especially thick in the palatal floor of the nasal 

 pharynx and similar to those of the oral cavity. 



The oral pharynx (figs. 848, 8G4, 888) is continuous above through the pharyn- 



