The former course is advocated by many general surgeons, the latter is the one usually pursued by the aural surgeon. The advantages claimed for the former method--the direct trephining method--are as follows:-- (1) The general condition of the patient is often of so serious a nature as to prohibit the more prolonged procedures essential to the mastoid exploration. (2) When the exploration is conducted from the infected middle ear, an unsuccessful attempt to find the abscess carries with it an appreciable risk of meningeal and brain infection. Unsuccessful exploration through the ‘clean’ squamous and cerebellar regions presents no such disadvantages. (3) The drainage as supplied through the trephine hole is often superior to that provided by dilating up the ‘stalk’ of the abscess into the middle ear. (4) Many general surgeons do not possess that intimate acquaintance with the anatomy of the ear which is necessary to carry out a complicated aural operation. Each case must be considered on its own merits, but I am inclined to advocate the two-stage method when the diagnosis is reasonably clear that the patient is suffering from temporo-sphenoidal or cerebellar abscess, mastoid exploration being carried out as soon as the patient has recovered from the first operation. When, however, considerable doubt exists as to the position of the abscess--or the nature of the complication in general--it is then advisable to start by exploration of the mastoid and aural regions, further measures being adopted according to the conditions found at the time of operation. 1. The two-stage operation. _Trephining for temporo-sphenoidal abscess._ A point is chosen on the scalp which lies between 1¹⁄₂ and 2 inches above the centre of the external auditory meatus, and a bradawl is there introduced so as to indent the external table of the skull. A small scalp-flap is framed, one presenting an upward convexity, and all bleeding controlled. The pin of the trephine is applied to the spot previously indicated on the bone and the disk removed. On account of the absence of diploic tissue and consequent approximation of the two tables of the skull, care must be taken to avoid injury to the posterior branch of the middle meningeal artery and to the bulging dura mater. [Illustration: FIG. 79. THE EXPOSURE OF A TEMPORO-SPHENOIDAL ABSCESS.] The dura is then inspected and palpated; absence of pulsation, loss of lustre and tenseness, indicate the probable adjacency of the abscess cavity. The membrane should be crucially incised, all meningeal vessels that cross the line proposed for section being first under-run on either side of that line. The scalpel is lightly applied to the membrane and, as soon as the pia-arachnoid is exposed, the section completed with the blunt-pointed scissors.