232 THE HEAD AND NECK 



laceration of the brain, the instrument must be kept closed while 

 it is being inserted and withdrawn. 



(e) In Ligature of the Posterior Division of the Middle 

 Meningeal Artery the skull is trephined at a point one inch above 

 and behind the external acoustic meatus. The skin incision is 

 planned so as to give good exposure of the area. 



The Approach to the Anterior Cranial Fossa may be 

 made from in front or from the side. In the latter case the 

 approach resembles that to the middle fossa, but the trephine 

 is applied farther forwards and sufficiently high to preclude 

 the possibility of opening through the lateral wall of the orbit. 



The operation is generally performed for abscess of the 

 frontal lobe, and it may be difficult to determine whether the 

 right or left side is involved. On this account the anterior route 

 may be preferred, as it enables the surgeon to expose the frontal 

 bone on both sides of the median line. The incision extends 

 from a little above the zygomatic (external angular) process of 

 the frontal bone on one side to a corresponding point on the 

 opposite side, and passes chiefly through the skin of the anterior 

 part of the scalp. In this way subsequent deformity due to 

 scarring may be avoided, and a large flap may be turned down- 

 wards. The trephine must be applied ij inches above the 

 superior margin of the orbit so as to avoid opening the frontal 

 air sinus. The subsequent procedure is very similar to that 

 described for the evacuation of an abscess in the temporal lobe. 



During the moulding of the fatal head at birth, the parietal 

 bones may overlap one another to such an extent as to cause 

 rupture of the superficial cerebral veins near their union with 

 the superior sagittal sinus. The subdural haemorrhage which 

 ensues is usually localised to the motor centre for the lower 

 limb (p. 229), and it gives rise to an irritative condition of the 

 cortex and to symptoms of cerebral compression. Unless these 

 signs are recognised and operation resorted to within ten days 

 or a fortnight, irreparable damage may be done to the brain. 

 Neglected cases of this kind give rise to one of the varieties of 

 " birth palsy " Little's disease. The haemorrhage may be 

 confined to one side only or it may be bilateral. 



A curved incision, which is carried down to the bone, is 

 made over the area and the flap is turned down. The thin 

 superior border of the parietal bone is exposed and a blunt 

 dissector is passed under it. An osseous flap, similar in shape 

 to but slightly smaller than the flap of soft parts, is made with 



