When should the common carotid artery be ligatured? How soon after the development of symptoms? This depends largely on the severity of the accident that produced the arterio-venous communication. If the blow was severe and the depth and duration of the stage of unconsciousness of a prolonged character, it may be presumed that the brain was injured. Under such circumstances early ligature of the common carotid presents an appreciable danger by reason of the development of hemiplegia on account of the further interference with the arterial supply to the brain. In such cases the patient should be confined to bed or kept quiet for not less than two months, the operation being carried out when the general condition warrants surgical interference. In the event of early operation being imperative, periodic digital compression of the common carotid, for a few minutes at a time, may be carried out with the object of accustoming the brain to the proposed new form of circulation. In ordinary cases the sooner the common carotid is tied the better is the ultimate result. [36] _Hunterian Lectures_, February 1904. [37] It is absolutely essential that the scalp incision should lie some distance away from the outer margin of the plate. Failure to adopt this procedure impedes the healing of the wound and adds to the risk of infection. [38] If desired, the plate may be anchored in position by means of a few small silver-plated screws. CHAPTER VII TUMOURS OF THE BRAIN =Tumours of the brain.= Tumours may develop in any part of the cerebrum and cerebellum, from the sheaths of the efferent nerves, from the vascular tissues, and from the membranes of the brain. Tumours arising from the bones of the skull are considered elsewhere (see p. 325). The regional distribution of these tumours may be estimated by reference to the following table[39]:-- Cerebellum 33 cases. Deep or subcortical 32 „ Precentral 30 „ Post-central 25 „ Extra-cerebellar 19 „ Pontine 15 „ Temporo-sphenoidal 13 „ Multiple 7 „ Fourth ventricle 5 „ Third ventricle 4 „ Pituitary 2 „ Schüster,[40] from an investigation of 1,000 cases, showed that cerebellar tumours are relatively more common than cerebral, the comparative size of the two regions being taken into account. An examination of Paton’s table shows that cerebellar and extra-cerebellar tumours together form rather more than 25 per cent. in 202 cases of brain-tumour formation. =Pathology.= Gliomata, sarcomata, and endotheliomata are the three commonest types of tumour formation. Other forms are fibromata, tuberculomata, syphilomata, cysts, and carcinomata. [Illustration: FIG. 62. A GLIOMA OF THE BRAIN.] [Illustration: FIG. 63. A SARCOMA OF THE BRAIN.]