The pharynx is a musculo-membranous sac which belongs to the digestive
and respiratory tracts in common. It is funnel-shaped, the base joining
the mouth and nasal cavity, while the apex is continued by the
œsophagus. Its long axis is directed obliquely downward and backward,
and has a length of about six inches (ca. 15 cm.).
The pharynx is attached by its muscles to the palate, pterygoid, and
hyoid bones, and to the cricoid and thyroid cartilages of the larynx.
Its principal =relations= are: dorsally, the base of the cranium and the
guttural pouches; ventrally, the larynx; laterally, the internal
pterygoid muscle, the great cornu of the hyoid bone, the internal and
external maxillary arteries, the glosso-pharyngeal, superior laryngeal,
and hypoglossal nerves, the submaxillary salivary gland, and the
pharyngeal lymph glands.
It presents =seven openings=. The =posterior nares= (Choanæ) communicate
dorsally with the nasal chambers. The pharyngeal orifices (Ostia
pharyngea) of the two =Eustachian tubes= are situated on the lateral
wall behind the nares and a little below the level of the inferior nasal
meatus. They are slit-like openings, slightly oblique downward and
backward, and are a little more than an inch (ca. 3 cm.) in length. They
are bounded internally by a valvular flap formed by the expanded
extremity of the cartilaginous Eustachian tube. The =isthmus faucium= is
situated below and in front. It is closed by the soft palate except
during swallowing. The =laryngeal orifice= (Aditus laryngis) occupies
the greater part of the ventral wall or floor of the pharynx. Behind
this is the =œsophageal opening=.
The wall of the pharynx comprises from without inward: the muscles, the
pharyngeal aponeurosis, and the mucous membrane.
The =muscles= (Figs. 243, 244) are covered by the pharyngeal fascia,
which is attached to the base of the skull, the great cornu of the hyoid
bone, and the thyroid cartilage of the larynx. They are as follows:
1. The =stylo-pharyngeus= arises from the inner surface of the dorsal
third of the great cornu of the hyoid bone, passes downward and inward,
and enters the wall of the pharynx by passing between the
pterygo-pharyngeus and palato-pharyngeus. Its fibers radiate, many
passing forward, others inward beneath the hyo-pharyngeus. It raises and
dilates the pharynx to receive the bolus in swallowing.
[Illustration:
FIG. 254.—POSTERIOR PART OF A SAGITTAL SECTION OF HEAD OF HORSE, CUT
ABOUT 1 CM. TO THE LEFT OF THE MEDIAN PLANE.
_1_, Posterior nares; _2_, pharyngeal orifice of Eustachian tube; _3_,
aditus laryngis; _4_, entrance to œsophagus; _5_, posterior pillar
of soft palate; _5′_, junction of _5_ with its fellow over entrance
to œsophagus; _6_, epiglottis; _7_, body of thyroid cartilage; _8_,
arytenoid cartilage; _9_, _9_, cricoid cartilage; _10_, true vocal
cord; _11_, false vocal cord; _12_, lateral ventricle of larynx;
_13_, crico-arytenoideus post. s. dorsalis; _14_, œsophagus; _15_,
external carotid artery; _16_, hypoglossal nerve; _17_,
glosso-pharyngeal nerve; _18_, great cornu of hyoid bone; _19_,
Eustachian tube; _20_, body of hyoid bone; _21_, hyoideus
transversus; _22_, ridges of hard palate; _22′_, soft palate; _23_,
septum between frontal sinuses; _24_, olfactory mucous membrane;
_25_, sphenoidal sinus; _26_, basilar part of occipital bone; _26′_,
supraoccipital; _27_, body of sphenoid bone; _28_, pituitary body;
_29_, chiasma opticum; _30_, corpora quadrigemina; _31_, thalamus;
_32_, arachnoid; _33_, odontoid ligament; _34_, posterior auricular
muscles.
]
2. The =palato-pharyngeus= arises by means of the aponeurosis of the
soft palate from the palate and pterygoid bones. Its fibers pass
backward on the lateral wall of the pharynx, and are inserted in part
into the upper edge of the thyroid cartilage, in part turn inward to end
at the median fibrous raphé. Its action is to shorten the pharynx, and
to draw the larynx and œsophagus toward the root of the tongue in
swallowing.
3. The =pterygo-pharyngeus= is flat and triangular. It lies on the
anterior part of the lateral wall of the pharynx. It arises from the
pterygoid bone above the preceding muscle—from which it is not
distinctly separated—crosses the levator palati, and is inserted into
the median raphé. Its action is similar to the preceding.