_‘Decompression’ operations._ ‘Decompression’ operations may be carried out over the cerebellar fossa or over the temporal region of the skull. In =cerebellar decompression= a suitable scalp-flap is turned down and the trephine applied over the centre of the exposed occipital bone. After the removal of the disk the wall of the cerebellar fossa is cut away with the craniectomy forceps, up to the line of the lateral sinus above, to the mastoid process in front, to the vicinity of the foramen magnum below, and almost up to the middle line on the inner side. The bulging dura mater is incised in a crucial manner, right up to the margins of the osseous gap, all meningeal vessels that cross the line proposed for dural section being under-run with a fully-curved needle threaded with catgut. A small drainage-tube is inserted between the dura and the cerebellum and brought out through the most dependent part of the scalp-flap. The flap is then sutured in position. The drainage-tube should be stitched to the skin and withdrawn twenty-four to forty-eight hours later, according to the progress of the case. I have carried out this operation on several occasions, but in spite of some immediate improvement in the condition of the patient, the remote results have been so unsatisfactory that I have abandoned the operation entirely. The effect of this cerebellar decompression is too radical, the medullary centres strongly object to such heroic attempts at pressure relief. _Temporal_ decompression, more correctly known as the =intermusculo-temporal decompression= operation of Harvey Cushing, leads to very different results. Previous to dealing with the technique of the operation, it will be convenient to enumerate the advantages claimed for this method in general. (1) The frequency with which the bony lesion occurs in the middle fossa of the skull. (2) The fact that cerebral contusions are especially liable to involve the tip of the temporo-sphenoidal lobe. (3) The exposure of the meningeal territory and the ease of determining the presence of an extra-dural hæmorrhage. (4) The possibility of draining through a split muscle rather than directly through the scalp. (5) The subsequent protective action of the muscle in case a hernia tends to form in consequence of traumatic œdema. (6) The subsequent absence of any deformities, the skin incision being carried out for the most part through the hairy portion of the scalp.