uniens.

#Congenital Sacro-coccygeal Tumours--Teratoma.#--Many varieties of
congenital tumours are met with in the region of the sacrum and
coccyx. The majority are developed in relation to the communication
which exists in the embryo between the neural canal and the alimentary
tract--the post-anal gut or neurenteric canal. Some are evidently of
bigerminal origin, and contain parts of organs, such as limbs, partly
or wholly formed, nerves, parts of eyes, mammary, renal, and other
tissues.

Among other tumours met with in this region may be mentioned: the
congenital _lipoma_--a small, rounded, fatty tumour which often
suggests a caudal appendage (Fig. 222); the _sacral hygroma_, which
forms a sessile cystic tumour growing over the back of the sacrum, and
is believed to be a meningocele which has become cut off _in utero_ by
the continued growth of the vertebral arch; dermoids, sarcoma, and
lymphangioma.

[Illustration: FIG. 223.--Congenital Sacro-coccygeal Tumour.

(Photograph lent by Sir George T. Beatson.)]

The _treatment_ consists in removing the tumour, as from its situation
it is exposed to injury, and this is liable to be followed by
infection. From the position of the wound, and the fact that many of
these tumours extend into the hollow of the sacrum and therefore
necessitate an extensive dissection, there is considerable risk from
infection, especially in young children. The risk is increased when
the tumour communicates with the vertebral canal.

#Congenital Sacro-coccygeal Sinuses and Fistulae.#--The _post-anal
dimple_, a shallow depression frequently observed over the tip of the
coccyx, may be due to traction exerted on the skin at this spot by the
remains of the neurenteric canal, or by the caudal ligament of
Luschka. Sometimes the integument is retracted to such an extent that
one or more _sinuses_ are formed, lined with skin which is furnished
with hairs, sweat, and sebaceous glands. The bursting of a dermoid, or
its being incised in mistake for an abscess, may result in the
formation of such a sinus, which fails to heal and may persist for
years.

In some cases the depression communicates with the vertebral canal,
constituting a complete _sacro-coccygeal fistula_, which may be lined
with cylindrical or ciliated epithelium.

From the accumulation of secretions and subsequent infection, these
conditions may be associated with a persistent offensive discharge,
and they are liable to be mistaken fo