argins, giving the appearance of
a combination of circles: these sometimes surround an area of bone and
cut it off from its blood supply (Fig. 130). If the overlying skin is
destroyed and septic infection superadded, such an isolated area of bone
is apt to die and furnish a sequestrum; the separation of the dead bone
is extremely slow, partly from the want of vascularity in the sclerosed
bone round about, and partly from the density of the sequestrum. In
exceptional cases the necrosis involves the entire vertical plate of the
frontal bone. Pus is formed between the bone and the dura (suppurative
pachymeningitis), and this may be followed by cerebral abscess or by
pyaemia. Gummatous disease in the wall of the orbit may cause
displacement of the eye and paralysis of the ocular muscles.

[Illustration: FIG. 130.--Syphilitic Disease of Skull, showing a
sequestrum in process of separation.]

On the inner surface of the skull, the formation of gummatous tissue may
cause pressure on the brain and give rise to intense pain in the head,
Jacksonian epilepsy, or paralysis, the symptoms varying with the seat
and extent of the disease. The cranial nerves may be pressed upon at the
base, especially at their points of exit, and this gives rise to
symptoms of irritation or paralysis in the area of distribution of the
nerves affected.

_In the septum of the nose, the nasal bones, and the hard palate_,
gummatous disease causes ulceration, which, beginning in the mucous
membrane, spreads to the bones, and being complicated with septic
infection leads to caries and necrosis. In the nose, the disease is
attended with stinking discharge (ozoena), the extrusion of portions of
dead bone, and subsequently with deformity characterised by loss of the
bridge of the nose; in the palate, it is common to have a perforation,
so that the air escapes through the nose in speaking, giving to the
voice a characteristic nasal tone.

_Syphilitic disease of the tibia_ may be taken as the type of the
affection as it occurs _in the long bones_. Gummatous disease in the
periosteum may be localised and result in the formation of a
well-defined node, or the whole shaft may become the seat of an
irregular nodular enlargement (Fig. 132). If the bone is macerated, it
is found to be heavier and bulkier than normal; there is diffuse
sclerosis with obliteration of the medullary canal, and the surface is
uneven from heaping up of new bone--hyperostosis (Fig. 131). If