ure, or drainage through the occipital fossa. The results,
however, have not been encouraging.

#Chronic Hydrocephalus.#--_Chronic external hydrocephalus_ is rare,
and usually results from some definite intra-cranial lesion, such as
meningitis, tumour, or cerebral atrophy. It is not amenable to
surgical treatment.

_Chronic internal hydrocephalus_, on the other hand, is a
comparatively common condition. It may be of congenital origin, or may
develop in young rickety children, usually as a result of some chronic
inflammatory process in the membranes at the base, the choroid
plexuses, or the ependyma of the ventricles, causing obstruction to
the outflow of blood through the internal cerebral veins of Galen. In
the acquired form the communication between the ventricles and the
sub-arachnoid space, by way of the foramen of Magendie, is obstructed,
so that the cerebro-spinal fluid is pent up in the ventricles and
gradually distends them. The pressure causes the head to enlarge, the
fontanelles to bulge, and the bones to be separated from one another,
the interval between the bones being occupied by a thin translucent
membrane.

The cerebral tissue is greatly thinned out, but the cerebellum and
cranial nerves usually remain unaffected.

The appearance of the patient is characteristic (Fig. 200). The
enormous dome of the skull surmounts a puny and preternaturally old
face; the eyes are pushed downwards and forwards by the pressure on
the orbital plates, and the eyebrows are displaced upwards. The head
rolls helplessly from side to side; the child moans and cries a great
deal; and vomiting is often a prominent symptom. In most cases the
intelligence is defective, and epileptic seizures and other functional
disturbances of the brain may be present.

[Illustration: FIG. 200.--Hydrocephalus in a child aet. 3-1/2.]

In mild cases, especially when associated with rickets or syphilis,
recovery sometimes takes place, but in the majority the condition
progresses, and death results either from convulsions or from some
intercurrent disease. Few hydrocephalic subjects reach adult life.

_Treatment._--Hydrocephalus being a symptom rather than a disease, no
method of treatment which does not remove the primary cause can be
permanently curative. Anti-syphilitic treatment should be tried in the
hydrocephalus of infants and young children. The rachitic element,
when present, must also be treated.

In congenital hydrocephalus, as ther