984 THE DIGESTIVE SYSTEM. 
contraction, an elevation just below the Eustachian orifice, known as the levator 
cushion (torus levatorius, Figs. 660 and 661), which in its outer portion abuts against 
the lower part of the orifice, and forms its base when that opening assumes its usual 
triangular shape. 
Occasionally the Eustachian orifice is of an oval or slit-like form, with sloping edges, 
but the triangular shape described above is much more commonly found. 
Immediately behind each Eustachian orifice is seen the lateral recess of the 
pharynx (recessus pharyngeus, fossa of Rosenmiiller), a nearly vertical, slit-like 
depression of considerable depth (Figs. 660 and 661), which runs outwards in the 
form of a flattened pouch or diverticulum. 
The lateral recesses project out over the upper margin of the superior constrictor, and 
beneath the petrous portion of the temporal bone, corresponding to the position of the sinus of 
Morgagni on each side. The recess is the remains of the inner or pharyngeal portion of the 
second visceral cleft, the lower part of which is represented in the supratonsillar fossa. 
Oral Pharynx (pars oralis).—This is the portion of the pharyngeal cavity which 
lies behind the mouth, and intervenes between the soft palate above and the 
superior aperture of the larynx below. Its anterior wall is occupied by the 
isthmus of the fauces, leading into the mouth; and below this by the pharyngeal 
portion of the tongue, almost vertical in direction. Its lateral wall (Fig. 661) 
presents a triangular area (sinus tonsillaris), bounded in front by the anterior 
palatine arch, behind by the posterior palatine arch, and below by the sides of the 
tongue in its pharyngeal portion. This area is occupied in the greater part of its 
extent by the tonsil, above which is found a depression, the supratonsillar fossa 
(Fig. 661), which is of considerable interest clinically. 
The posterior palatine arch (arcus pharyngo-palatinus, posterior pillar of the 
fauces) is a prominent fold of mucous membrane, containing the palato-pharyngeus 
muscle in its interior, which springs above from the posterior edge of the soft 
palate, and, passing downwards and slightly backwards, ends below on the side-wall 
of the pharynx (Fig. 661). The two. 
posterior palatine arches form the 
lateral boundaries of the pharyngeal 
ee ce isthmus, which passage they can 
es modify both in size and shape by the 
R — contraction of their contained muscles. 
a. Posterior The anterior palatine arch is de- 
go% Palatinearch scribed on page 950. 
i _— The philtrum 
eae The pharyngeal isthmus (isthmus 
3 SS) 5 e . 
Tonsil pharyngo-nasalis) is the very oblique 
Anterior and somewhat triangular orifice 
palatineareh” through which the oral pharynx com- 
municates with the naso- pharynx 
oe (Fig. 663). It differs considerably in 
size and shape in different individuals, 
being in some so small that the naso- 
pharynx can be explored from the 
mouth only with very great difficulty ; 
whilst in others it is of much larger 
dimensions (Fig. 662) and affords ample 
space for the rhinoscopic examination 
of the naso-pharynx and the back part 
Fic. 663.—OPEN Moutd sHOWING PALATE AND TONSILS. of the nasal eavities 
It also shows the two palatine arches, and the pharyngeal In general it may be deseribed as 
isthmus through which the naso-pharynx above com- triangular in shape, the sides corre- 
municates with the oral portion of the pharynx 
Helga sponding to the posterior palatine 
arches, and the base, which is behind, 
being formed by the posterior wall of the pharynx. The apex of the triangle is 
directed towards the sott palate, and is encroached upon, and overlapped from below 
by, the uvula, which assists in the closure of the orifice (Fig. 663). 
