=Symptomatology.= (_a_) _Symptoms dependent on the formation of the thrombus and its extension to neighbouring venous and lymphatic channels._ The presence of the thrombus and its extension into ophthalmic, angular, and retinal veins leads to proptosis, paresis of the ocular muscles, disturbances of vision, and œdema. _Proptosis_ is of rapid development, frequently reaching its maximum within a few hours, the globe being protruded in the downward and outward direction. With respect to _ocular palsies_, the movements of the globe are greatly restricted with squints, ptosis, and perhaps complete ophthalmoplegia. The pupil may be contracted during the earlier stages, becoming fully dilated and insensitive at a later date. The _vision_ suffers in proportion to the degree of paralysis of ocular muscles and associated retinal hæmorrhages and thrombosis. The veins of the lids, conjunctivæ, and upper part of the face and forehead are engorged, with corresponding œdema of the soft parts. The conjunctivæ may be chemotic. The spread of the thrombus to the opposite sinus results in the development of bilateral symptoms, whilst the involvement of the petrosal sinus may bring about thrombosis of the lateral and sigmoid sinuses, with corresponding developments. In other cases the meningeal veins are affected at an early date, in which case the symptoms dependent on the cavernous thrombus are obscured by those resulting from the meningeal infection. (_b_) _Symptoms dependent on toxic absorption or resulting from the transference of infected particles to other parts of the body._ These more general symptoms closely resemble those enumerated when discussing lateral sinus thrombosis (see p. 283). Headache, however, is of the most intense type, and pain, of a severe neuralgic character, is referred along the course and distribution of the first and second divisions of the fifth nerve. =Treatment.= It has been suggested that exploration could be carried out, the thrombus evacuated, and the cavernous sinus region drained from the naso-ethmoidal region or by approach along the floor of the middle fossa of the skull--an exaggerated Gasserian ganglion operation. Both these methods have been tried, but the difficulties encountered and the want of success tended to show that cavernous sinus thrombosis was beyond the reach of the surgeon. However, of recent date, more hopeful views have been entertained, it being suggested that the globe should be removed, the sinus explored, and the orbital cavity packed with gauze. It is doubtful, however, whether the end justifies the means.