The _cavernous sinus_ is usually implicated by spread of the process from other sinuses--for instance, from the petrosal or transverse (lateral) sinuses--or from the ophthalmic veins in cases of orbital cellulitis. Although at first unilateral, the thrombosis usually spreads across the middle line to the sinus of the opposite side. The special symptoms--exophthalmos, œdema of the eyelids, and paralysis of the ocular nerves--are due to pressure on the structures entering the orbit. Operative interference is seldom feasible in phlebitis of the superior sagittal (longitudinal) or cavernous sinuses. #Intra-cranial Tuberculosis.#--_Tuberculous meningitis_ is most frequently met with in patients below the age of twenty, and the infection takes place by the blood stream from some focus elsewhere in the body or from the spinal membranes. In cases of tuberculous disease of the middle ear infection may spread to the membranes by way of the internal auditory meatus (Macewen). The arachno-pia, especially at the base, is studded over with miliary tubercles, and an excess of fluid collects in the arachno-pial space and in the ventricles (_acute hydrocephalus_). At first the _symptoms_ of irritation of the brain predominate: severe headache, photophobia, inequality of the pupils, stiffness of the neck, cutaneous hyperæsthesia, vomiting and convulsions. Kernig's sign--pain on flexing the hip while the knee is extended, and inability to extend the knee while in the sitting posture--is present. There is usually obstinate constipation, and the abdomen is retracted. Later, signs of increased intra-cranial tension develop: unconsciousness deepening into coma, paralysis of ocular muscles, rapid pulse, Cheyne-Stokes respiration, and sometimes hyperpyrexia. An excess of mono-nuclear lymphocytes and, sometimes, tubercle bacilli may be discovered in the cerebro-spinal fluid withdrawn by lumbar puncture. The absence of the diplococcus intracellularis helps to differentiate the disease from cerebro-spinal meningitis, which it may closely simulate. The only surgical measure that is justifiable is lumbar puncture, which often affords marked relief of symptoms, although the benefit is only temporary. _Localised tuberculous nodules_ sometimes develop in the brain and form definite tumours. They vary in size from a pea to a hen's egg, are rounded and encapsulated. Sometimes the centre is caseous, sometimes fibrinous or calcified. In children they are usually multiple; in adults they may be single--the so-called "solitary tubercle." They are most common in the pons, basal ganglia, and cerebellum, but occur also in the cerebral cortex and sometimes in the centrum ovale. They usually originate in the pia and invade the brain substance, but do not as a rule involve the dura. The membranes in the vicinity of the growth are often the seat of tuberculous disease.