ecesses, known as post-anal dimples and coccygeal sinuses.
These recesses are lined with skin, which is furnished with hairs,
sebaceous and sweat glands. If the external orifice becomes occluded,
there results a dermoid cyst.

_Tubulo-dermoids_ arise from embryonic ducts and passages that are
normally obliterated at birth, for example, _lingual dermoids_ develop
in relation to the thyreo-glossal duct; _rectal and post-rectal_
dermoids to the post-anal gut; and _branchial dermoids_ in relation to
the branchial clefts. Tubulo-dermoids present the same structure as skin
dermoids, save that mucous membrane takes the place of skin in the wall
of the cyst, and the contents consist of the pent-up secretion of mucous
glands.

_Clinical Features._--Although dermoids are of congenital origin, they
are rarely evident at birth, and may not give rise to visible tumours
until puberty, when the skin and its appendages become more active, or
not till adult life. Superficial dermoids, such as those met with at the
outer angle of the orbit, form rounded, definitely limited tumours over
which the skin is freely movable. They are usually adherent to the
deeper parts, and when situated over the skull may be lodged in a
depression or actual gap in the bone. Sometimes the cyst becomes
infected and suppurates, and finally ruptures on the surface. This may
lead to a natural cure, or a persistent sinus may form. Dermoids more
deeply placed, such as those within the thorax, or those situated
between the rectum and sacrum, give rise to difficulty in diagnosis,
even with the help of the X-rays, and their nature is seldom recognised
until the escape of the contents--particularly hairs--supplies the clue.
The literature of dermoid cysts is full of accounts of puzzling tumours
met with in all sorts of situations.

The treatment is to remove the cyst. When it is impossible to remove the
whole of the lining membrane by dissection, the portion that is left
should be destroyed with the cautery.

_Ovarian Dermoids._--Dermoids are not uncommon in the ovary (Fig. 59).
They usually take the form of unilocular or multilocular cysts, the
wall of which contains skin, mucous membrane, hair follicles, sebaceous,
sweat, and mucous glands, nails, teeth, nipples, and mammary glands. The
cavity of the cyst usually contains a pultaceous mixture of shed
epithelium, fluid fat, and hair. If the cyst ruptures, the epithelial
elements are diffused over the peritoneum, a