This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
This is the depression above and behind the openings of the Eustachian tubes. The walls of the pharynx are weakest at this point owing to the superior constrictor muscle not coming so high up. Hernia of the mucous membrane sometimes occurs here. When the beak of the Eustachian catheter fails to enter the mouth of the tube it usually enters this fossa.
The internal carotid artery runs up the neck outside of the pharynx and opposite the space between the posterior arches of the palate and the posterior wall of the pharynx. It is from 1 to 2 cm. behind and to the outer side of the tonsils. It is separated from the cavity of the throat by its own proper sheath, by the thin buccopharyngeal fascia covering the constrictor muscles, by the constrictor muscles, the pharyngeal aponeurosis, and the mucous membrane. As the tonsils lie between the pillars of the fauces, in opening a tonsillar abscess the knife is not carried either behind or through the posterior pillar of the fauces. It is practically impossible to wound a normal internal carotid artery. In old people the internal carotid sometimes becomes lengthened and tortuous in the same manner as do the temporal arteries. In such cases the artery may form a pulsating swelling behind and projecting farther inward than the edge of the posterior pillar. This I have once seen. It may be mistaken for a true aneurism, as it pulsates and the pulsation is readily stopped by pressure on the common carotid on the outside of the neck. If, however, the possibility of this condition is borne in mind, the diagnosis can readily be made. The pulsating swelling can readily be seen and felt with the finger just behind the posterior pillar of the fauces.
Fig. 156. - Transverse dissection of the neck. The posterior wall of the pharynx has been removed and the vessels exposed. The internal carotids are seen to be abnormally tortuous, with a tendency to bulge into the pharynx.
The mucous membrane of the nasopharynx is ciliated columnar; that of the lower portion is squamous. It contains racemose mucous glands and follicles or crypts surrounded by lymphoid tissue. It is well supplied with blood-vessels. It is frequently affected by inflammation or pharyngitis. When the follicles are markedly involved they can be seen studded over the posterior wall of the pharynx. This constitutes a follicular pharyngitis. Not infrequently some ulceration may be present, forming an ulcerative pharyngitis. Infection attacks it, as in diphtheritic pharyngitis. Should pus or pharyngeal abscess form around the pharynx, arising from an infection from the oral cavity, the pus occupies the retropharyngeal space between the buccopharyngeal fascia and prevertebral fascia. Its spread upward is limited by the skull; laterally it is limited by the sheath of the carotid vessels; hence it passes downward behind the oesophagus and may enter the posterior mediastinum. Foreign bodies may become lodged at the lower end of the pharynx and at the beginning of the oesophagus. As this is about 15 cm. (6 in.) from the teeth, it is beyond the reach of the ringer. Luckily, this is below the opening of the larynx and the need for immediate relief is not so urgent.