#Tumours of the Mandible.#--The same varieties are met with as in the
maxilla. The non-malignant forms--osteoma, chondroma, and fibroma--are
rare.

A _dentigerous cyst_ appears as a smooth, rounded, and painless
swelling, usually in the region of the molar teeth. The bone gradually
becomes expanded and crackles on pressure. The cyst is filled with a
glairy mucoid fluid, and may contain one or more unerupted teeth (Fig.
252). The X-ray appearances are characteristic. The treatment consists
in removing the anterior wall of the cyst, scraping the interior, and
packing the cavity with iodoform or bismuth gauze.

[Illustration: FIG. 252.--Dentigerous Cyst of Mandible containing
rudimentary tooth.

(From Sir Patrick Heron Watson's collection.)]

The myeloid tumour or _myeloma_ is comparatively common. It develops
in the interior of the bone and expands the affected segment (Fig.
253). It grows slowly, is more or less encapsulated, and therefore
does not infiltrate the surrounding tissues. Sometimes it so weakens
the bone that pathological fracture occurs. There is no glandular
involvement, and the tumour shows little evidence of malignancy.

[Illustration: FIG. 253.--Osseous Shell of Myeloma of Mandible.

(From Professor Annandale's collection.)]

The _periosteal sarcoma_ is the most malignant form. It grows rapidly,
and infiltrates the surrounding tissues. The submaxillary salivary
glands and the cervical lymph glands are usually implicated, and the
disease tends to spread by metastasis to distant parts.

_Epithelioma_ is the commonest new growth affecting the mandible; it
usually involves the central portion of the bone, being a direct
spread from the lower lip, tongue, or floor of the mouth. When it
originates in the pillars of the fauces it implicates the ascending
ramus. In all cases the infection of the cervical lymph glands is a
serious factor both in prognosis and treatment.

_Treatment._--_Partial removal_ of the mandible may be undertaken for
myeloma, and in cases of sarcoma and epithelioma in which the tumour
is limited to a small area of the bone--for example, to the alveolar
process, the angle, the horizontal ramus, or the symphysis; in other
cases, the whole bone must be removed.

INJURIES OF THE JAWS

#Fracture of the Maxilla.#--Fractures of the maxilla are nearly always
due to direct violence, such as a blow on the face, a stab, or a
gun-shot wound. They are often rendered compound by opening