medullary_), in the membranes
(_meningeal_), or in the tissues between the dura and the bone
(_extra-dural_); or the cord may be pressed upon by a tumour
originating in the vertebrae. It is seldom possible to diagnose the
nature of a tumour before operation, and it is often difficult to
determine in which of the above situations it has originated.

Tumours growing _in the substance of the cord_ are nearly as common
as extra-medullary growths, and as the growth is usually sarcoma,
glioma, tuberculoma, or gumma, and infiltrates the cord, it is seldom
capable of being removed by operation.

The great majority of _meningeal_ tumours are primary sarcomas, and in
about 25 per cent. of cases they are multiple. Hydatid cysts and
fibromas are also met with in this situation, and they too may be
multiple.

_Extra-dural_ growths are comparatively rare. The forms usually met
with are sarcoma and lipoma.

These extra-medullary tumours seldom infiltrate the cord; they simply
compress it, and should be subjected to operative treatment before
secondary changes are produced in the cord.

The _symptoms_ vary according as the tumour presses on the nerve
roots, on one half, or on both halves of the cord. Pressure on nerve
roots is a characteristic sign in extra-medullary growths. It gives
rise to pain, which, according to the level of the tumour, passes
round the trunk (girdle-pain), or shoots along the nerve-trunks of the
upper or lower limbs.

When the cord is pressed upon, intense neuralgic pain related to the
segment first involved is one of the earliest symptoms, particularly
in extra-medullary tumours. The pain is at first unilateral, but later
becomes bilateral--a point of importance in diagnosis. The painful
areas are anaesthetic, but the anaesthesia does not always reach to the
level of the lesion. There may be a zone of hyperaesthesia at the upper
limit of the anaesthesia, or in the area corresponding to the roots on
which the tumour is situated, but there is never diffuse hyperaesthesia
(V. Horsley). In intra-medullary tumours the pain is less severe, it
is rarely an initial symptom, and is seldom referable to individual
nerve roots.

The next symptom to appear is motor paresis, followed by complete
paralysis, and later by contracture of the paralysed muscles--_spastic
paraplegia_. In intra-medullary tumours the paraplegia is usually less
complete than in those that are extra-medullary. When only one lateral
half of th