ually
form in connection with the third cleft, and are met with in the
region of the great cornu of the hyoid bone, to which the wall of the
cyst is almost always attached. Less frequently they take origin in
the second cleft, and lie below the mastoid process, in which case the
cyst is adherent either to the mastoid or to the styloid process. In
some cases these cysts project towards the floor of the mouth. When
near the skin they are of the nature of _dermoid cysts_, being lined
with squamous epithelium and filled with sebaceous material. When
deeply placed, they are lined by cylindrical or ciliated epithelium
and contain a glairy mucoid fluid.

Although of congenital origin, these cysts do not usually attract
attention till about the age of puberty, when they are noticed as
small, soft, fluctuating tumours over which the skin moves freely.
They grow slowly, but may attain great dimensions. The only treatment
that yields satisfactory results is complete excision.

The _cystic lymphangioma_, _hygroma_, or _hydrocele of the neck_ (Fig.
274), has been described with affections of lymphatics (Volume I., p.
327); and _thyreo-glossal cysts in the neck_ at p. 583.

[Illustration: FIG. 274.--Hygroma of Neck.

(Photograph lent by Mr. J. W. Dowden.)]

_Blood Cysts._--These may originate in a diverticulum of a vein that
has become isolated, or in a cavernous angioma; or they may be due to
haemorrhage taking place into a branchial or thyreo-glossal cyst. The
diagnosis is often only possible by exploratory puncture; and the
treatment consists in complete excision.

_Cystic Bursae._--Cystic degeneration may occur in the supra-hyoid and
thyreo-hyoid bursae, and give rise to a rounded swelling which moves
with the thyreoid on swallowing, and is only troublesome from the
disfigurement it causes. It is treated by excision.

#Solid Tumours#, apart from the common enlargements of lymph glands,
and the various forms of goitre, are not often met with in the neck.

The _circumscribed lipoma_ usually occurs over the nape of the neck or
in the supra-clavicular region. It may attain considerable size, and
from its weight become pedunculated and hang down over the back or
shoulder.

_Diffuse lipomatosis_ usually begins over the nape and spreads more or
less symmetrically till it completely surrounds the neck. As the
new-formed fat is not encapsulated, extirpation of the mass is
difficult and is seldom called for.

[Illustration: FI