ed into the axilla. The anterior or _muscular
compartment_ contains the sterno-mastoid muscle and the depressor
muscles of the hyoid bone. It extends upwards as far as the hyoid bone
and base of the mandible, and downwards as far as the sternum and
clavicle. The arrangement and limits of the different layers of the
cervical fascia explain the course taken by inflammatory products and
by new growths in the neck.

#Malformations of the Neck.#--Various congenital deformities result
from interference with the developmental processes which take place in
and around the fore-gut. These malformations are associated chiefly
with imperfect development of the visceral or branchial arches and
clefts, or of the hypoblastic diverticula from which the thyreoid and
thymus glands are formed.

The term _cervical auricles_ is applied to small outgrowths, composed
of skin, connective tissue, and yellow elastic cartilage, found
usually along the anterior border of the sterno-mastoid. These
appendages are usually unilateral, and are derived from the second
visceral arch. Sometimes they are situated near the orifice of a
lateral fistula. When, on account of their size, or their situation on
an exposed part of the neck, they give rise to disfigurement, they
should be removed.

_Thyreo-glossal Cysts and Fistulae._--The thyreo-glossal _cyst_ is
developed in relation to the thyreo-glossal tract of His, which in
early embryonic life extends from the foramen caecum at the base of the
tongue to the isthmus of the thyreoid. Those that form in the upper
part of the tract, in relation to the base of the tongue, have already
been described (p. 538). Those arising from the lower part form a
swelling in the middle line of the neck, usually above, but sometimes
below the hyoid bone. They have to be diagnosed from other forms of
cyst occurring in the middle line of the neck--sebaceous and dermoid
cysts--and when giving rise to disfigurement they should be excised.

Such a cyst may rupture on the surface, usually as a result of
superadded infection, and give rise to a _thyreo-glossal_ or _median
fistula of the neck_. As a rule the external opening of the fistula is
above the hyoid bone, only the upper part of the duct having remained
pervious. When the whole length of the duct has persisted, the fistula
extends from the skin to the foramen caecum, passing usually in front
of, but sometimes through the substance of, the hyoid bone.
Occasionally the fistu