THE BRAIN AND ITS MENINGES 231 



removed the opening is enlarged by means of craniectomy 

 forceps. The inner blade of this instrument is blunt, and 

 formed so as to separate the dura mater from the inner surface 

 of the skull while the bone is being removed. 



(a) In Ligature of the Anterior Division or of the Main 

 Trunk of the Middle Meningeal Artery the trephine is applied 

 over the Sylvian point (p. 229), and, when the disc of bone is 

 removed,, the anterior division is exposed running upwards over 

 the dura mater. Not infrequently the artery lies in a small 

 canal on the deep surface of the bone, and in these cases a seg- 

 ment of the vessel will be removed along with the disc of bone. 

 The opening must then be enlarged in a downward direction 

 until the vessel is found leaving the canal, when its proximal 

 end can be ligated. 



(b) The operation of Temporal Decompression is undertaken 

 to relieve the symptoms of headache and progressive loss of 

 vision, which result from increased intra-cranial pressure due 

 to cerebral tumours. The trephine is applied behind the Sylvian 

 point in order to avoid the anterior branch of the middle menin- 

 geal artery. The opening is enlarged in a downward and 

 backward direction till its diameter has been increased to from 

 2\ to 3 inches. While this enlargement is being carried out 

 the posterior division of the middle meningeal artery is exposed. 

 A crucial incision is made in the bulging dura mater after all 

 the vessels which are likely to be cut have been secured. 



(c) The approach to the Semilunar (Gasserian) Ganglion is 

 described on p. 234. 



(d) In order to evacuate an Abscess of the Temporal Lobe 

 a trephine opening is made at a point two inches above the ex- 

 ternal acoustic meatus. The skin incision begins in front of the 

 auricle, and is carried upwards and backwards above it and then 

 downwards behind it. After the membranes have been opened, 

 a director is passed medially into the brain at the point where 

 it bulges most. If the abscess is not located the director is 

 withdrawn, and then passed forwards and medially or back- 

 wards and medially until pus is found. Throughout the ex- 

 ploration the instrument should be kept parallel to the tegmen 

 tympani, and it must not be inserted for more than i inches 

 lest the inferior (descending) horn of the lateral ventricle be 

 entered. When Horsley's pus evacuator is used in place of a 

 director, it must be passed in closed, and it should be opened at 

 intervals of a quarter of an inch. In order to prevent severe 



