gioma_. It is
probable that the cysts are derived from the caverns by breaking down
and absorption of the intervening septa, as transition forms between the
cavernous and cystic varieties are sometimes met with.

The _cavernous lymphangioma_ appears as an ill-defined, soft swelling,
presenting many of the characters of a subcutaneous haemangioma, but it
is not capable of being emptied by pressure, it does not become tense
when the blood pressure is raised, as in crying, and if the tumour is
punctured, it yields lymph instead of blood. It also resembles a lipoma,
especially the congenital variety which grows from the periosteum, and
the differential diagnosis between these is rarely completed until the
swelling is punctured or explored by operation. If treatment is called
for, it is carried out on the same lines as for haemangioma, by means of
electrolysis, igni-puncture, or excision. Complete excision is rarely
possible because of the want of definition and encapsulation, but it is
not necessary for cure, as the parts that remain undergo cicatrisation.

[Illustration: FIG. 76.--Congenital Cystic Tumour or Hygroma of Axilla.

(From a photograph lent by Dr. Lediard.)]

The _cystic lymphangioma_, _lymphatic cyst_, or _congenital cystic
hygroma_ is most often met with in the neck--_hydrocele of the neck_; it
is situated beneath the deep fascia, and projects either in front of or
behind the sterno-mastoid muscle. It may attain a large size, the
overlying skin and cyst wall may be so thin as to be translucent, and it
has been known to cause serious impairment of respiration through
pressing on the trachea. In the axilla also the cystic tumour may attain
a considerable size (Fig. 76); less frequent situations are the groin,
and the floor of the mouth, where it constitutes one form of ranula.

The nature of these swellings is to be recognised by their situation, by
their having existed from infancy, and, if necessary, by drawing off
some of the contents of the cyst through a fine needle. They are usually
remarkably indolent, persisting often for a long term of years without
change, and, like the haemangioma, they sometimes undergo spontaneous
cicatrisation and cure. Sometimes the cystic tumour becomes infected and
forms an abscess--another, although less desirable, method of cure.
Those situated in the neck are most liable to suppurate, probably
because of pyogenic organisms being brought to them by the lymphatics
taking or