s of a gag, the head allowed to hang over the
end of the table, and the abscess incised, with a guarded bistoury,
through the wall of the pharynx. The dangers associated with opening
the abscess from the mouth appear to have been exaggerated.

A _less acute_ form of retro-pharyngeal abscess sometimes develops in
the course of chronic middle ear disease, the inflammatory process
spreading along the Eustachian tube, in the wall of which an abscess
forms and burrows into the retro-pharyngeal space.

CHAPTER XXI

THE JAWS, INCLUDING THE TEETH AND GUMS

TEETH: Dental caries--Impacted wisdom tooth. GUMS: Gingivitis;
Pyorrhoea alveolaris; Hypertrophy; Epithelioma. JAWS: Pyogenic
affections: _Periostitis_; _Osteomyelitis_; Tuberculosis;
Syphilis; Actinomycosis--Tumours: _Of alveolar process_; _Of
maxilla_; _Of mandible_--Fracture of maxilla--Fracture of
mandible--Affections of the temporo-mandibular articulation:
_Dislocation of the mandible_; _Acute arthritis_; _Tuberculous
arthritis_; _Arthritis deformans_; _Closure of the jaws_.

#Dental caries# is a process of disintegration which begins in the
enamel of a tooth--usually in the region of its neck--and gradually
extends through the dentine till the pulp cavity is reached.

Infection of the exposed pulp cavity may set up an acute purulent
_pulpitis_. This is associated with severe pain, which is not confined
to the diseased tooth, but may spread to adjacent teeth, and sometimes
to all the branches of the trigeminal nerve on the same side of the
face.

The infection may spread from the tooth to the alveolo-dental
periosteum, and set up a _periodontitis_. In the affected tooth there
is at first a feeling of uneasiness, which is relieved by the patient
biting against it. Later there is severe lancinating or throbbing
pain. The affected tooth usually projects beyond its neighbours, and
is excessively tender when the opposing tooth comes in contact with it
in mastication. The gum becomes red and swollen, and the cheek is
oedematous.

Periodontitis is usually followed by the formation of an _alveolar
abscess_. The pus, which forms at the root of the tooth, in most cases
works its way through the bone and into the gum, constituting a
"gum-boil." The pus may then burst through the gum, or may spread
underneath the external periosteum of the jaw and lead to necrosis.

In some cases the cheek becomes adherent to the gum and to the jaw
bef