chiefly injurious if they are accompanied by lesions of
the underlying dura, such as adhesions to the brain; large gaps may
cause giddiness on stooping, or on forcible expiration, as in blowing
the nose or playing a wind instrument.

#Varieties.#--For descriptive purposes, fractures of the vault are
divided into the fissured, the punctured, the depressed, and the
comminuted varieties. Clinically, however, these varieties are often
combined. The practical importance of a given fracture depends upon
whether it is simple or compound, rather than upon the exact nature of
the damage done to the bone. Compound fractures which open the dura
mater are the most serious. Simple fractures result, as a rule, from
diffuse forms of violence, and are liable to spread far beyond the
seat of impact. Compound fractures result from severe and localised
violence--for example, the kick of a horse or the blow of a
hammer--and tend to be limited more or less to the seat of impact. In
gun-shot injuries, however, there are usually numerous fissures
radiating from the point at which the missile enters the skull.

#Fissured fractures# generally result from blows by blunt objects or
from falls, and they usually extend far beyond the area struck, in
most cases passing into the base. The fissure may pass through the
bone vertically or obliquely, and it may implicate one or both tables.
So long as the fracture is simple, it can scarcely be diagnosed except
by inference from the associated symptoms of meningeal or cerebral
injury. When compound, the crack in the bone can be seen and felt. It
is recognised by the eye as a split in the bone, filled with red
blood, which, as often as it is sponged away, oozes again into the
gap. In fractures by bursting a tuft of hair may be caught between the
edges of the fracture, and this adds to the difficulty of purifying
the wound.

_Diagnosis._--A normal suture may be mistaken for a fissured fracture.
A suture, however, may generally be recognised by its position, the
irregularity of its margins, and the absence of blood between its
edges. At the same time, it is not uncommon, especially in children,
for a suture to be sprung by violence applied to the head, or for a
fissured fracture to enter a suture and, after running in it for some
distance, to leave it again. The edges of a clean cut in the
periosteum may be mistaken for a fissure in the bone, especially if
reliance is placed on the probe for diagnosis. Th