ncer will be
considered with regional surgery.

_Secondary sarcoma_ is seldom met with in the lymph glands except when
the primary growth is a lympho-sarcoma and is situated in the tonsil,
thyreoid, or testicle.

CHAPTER XVI

THE NERVES

Anatomy--INJURIES OF NERVES: Changes in nerves after division;
Repair and its modifications; Clinical features; _Primary and
secondary suture_--SUBCUTANEOUS INJURIES OF
NERVES--DISEASES: _Neuritis_; _Tumours_--Surgery of
the individual nerves: _Brachial neuralgia_; _Sciatica_;
_Trigeminal neuralgia_.

#Anatomy.#--A nerve-trunk is made up of a variable number of bundles of
nerve fibres surrounded and supported by a framework of connective
tissue. The nerve fibres are chiefly of the medullated type, and they
run without interruption from a nerve cell or _neuron_ in the brain or
spinal medulla to their peripheral terminations in muscle, skin, and
secretory glands.

Each nerve fibre consists of a number of nerve fibrils collected into a
central bundle--the axis cylinder--which is surrounded by an envelope,
the neurolemma or sheath of Schwann. Between the neurolemma and the axis
cylinder is the medullated sheath, composed of a fatty substance known
as myelin. This medullated sheath is interrupted at the nodes of
Ranvier, and in each internode is a nucleus lying between the myelin and
the neurolemma. The axis cylinder is the essential conducting structure
of the nerve, while the neurolemma and the myelin act as insulating
agents. The axis cylinder depends for its nutrition on the central
neuron with which it is connected, and from which it originally
developed, and it degenerates if it is separated from its neuron.

The connective-tissue framework of a nerve-trunk consists of the
_perineurium_, or general sheath, which surrounds all the bundles; the
_epineurium_, surrounding individual groups of bundles; and the
_endoneurium_, a delicate connective tissue separating the individual
nerve fibres. The blood vessels and lymphatics run in these
connective-tissue sheaths.

According to Head and his co-workers, Sherren and Rivers, the afferent
fibres in the peripheral nerves can be divided into three systems:--

1. Those which subserve _deep sensibility_ and conduct the impulses
produced by pressure as well as those which enable the patient to
recognise the position of a joint on passive movement (joint-sensation),
and the kinaesthetic sense, which recognises