nd may give rise to
secondary dermoids.

[Illustration: FIG. 59.--Dermoid Cyst of Ovary showing Teeth in its
interior.]

The ovarian dermoid appears clinically as an abdominal or pelvic tumour
provided with a pedicle; if the pedicle becomes twisted, the tumour
undergoes strangulation, an event which is attended with urgent
symptoms, not unlike those of strangulated hernia.

The treatment consists in removing the tumour by laparotomy.

#Teratoma.#--A teratoma is believed to result from partial dichotomy or
cleavage of the trunk axis of the embryo, and is found exclusively in
connection with the skull and vertebral column. It may take the form of
a monstrosity such as conjoined twins or a parasitic foetus, but more
commonly it is met with as an irregularly shaped tumour, usually growing
from the sacrum. On dissection, such a tumour is found to contain a
curious mixture of tissues--bones, skin, and portions of viscera, such
as the intestine or liver. The question of the removal of the tumour
requires to be considered in relation to the conditions present in each
individual case.

CYSTS[3]

[3] Cysts which form in relation to new-growths have been considered
with tumours.

Cysts are rounded sacs, the wall being composed of fibrous tissue lined
by epithelium or endothelium; the contents are fluid or semi-solid, and
vary in character according to the tissue in which the cyst has
originated.

_Retention and Exudation Cysts._--_Retention cysts_ develop when the
duct of a secreting gland is partly obstructed; the secretion
accumulates, and the gland and its duct become distended into a cyst.
They are met with in the mamma and in the salivary glands. Sebaceous
cysts or wens are described with diseases of the skin. _Exudation cysts_
arise from the distension of cavities which are not provided with
excretory ducts, such as those in the thyreoid.

_Implantation cysts_ are caused by the accidental transference of
portions of the epidermis into the underlying connective tissue, as may
occur in wounds by needles, awls, forks, or thorns. The implanted
epidermis proliferates and forms a small cyst. They are met with chiefly
on the palmar aspect of the fingers, and vary in size from a split pea
to a cherry. The treatment consists in removing them by dissection.

_Parasitic cysts_ are produced by the growth within the tissues of
cyst-forming parasites, the best known being the taenia echinococcus,
which gives rise to the _h