442 



THE PINEAL ORGAN 



burr holes are made in the skull at the periphery of the scalp incision and 

 these burr holes are joined by means of a Gigli saw, which is inserted 

 by a special curved introducer (Fig. 290). After the saw has been intro- 

 duced, the bone between the burr holes is cut on the bevel, the intro- 

 ducers acting as a protector to the underlying dura mater and brain 

 (Fig. 291). When all the burr holes have been united with the exception 

 of the lowest two, the osteoplastic flap can be elevated and fractured 

 across its narrow and thinned-out base ; it is then hinged outwards on 

 the temporal muscle. Bleeding vessels in the dura mater are underrun 



Fig. 290. — Useful Gigli Saw 

 Guide. 



Fig. 291. — The Method of Introduc- 

 ing a Gigli Saw between Two 

 Burr Holes. 



with silk sutures, while those occurring in the bone are controlled with 

 Horsley's bone wax. If there is a considerable increase of the intra- 

 cranial pressure this can be diminished by the administration of 20 c.c. 

 of hypertonic saline (15 per cent.) at the commencement of the operation, 

 but as a rule this is not necessary because adequate reduction of the intra- 

 cranial pressure may be produced by tapping the lateral ventricle. It is 

 a remarkable fact that although an internal hydrocephalus causes gradual 

 destruction of cerebral tissue, yet this hydrocephalus is advantageous to 

 the surgeon when removing a pineal tumour ; otherwise it would be 

 impossible to retract the posterior part of a normal hemisphere without 

 causing some permanent damage. When the fluid from the ventricle 

 is withdrawn in a case of internal hydrocephalus, the flattened-out hemi- 

 sphere can be retracted without further damage ensuing. 



A flap of dura mater is turned outwards on top of the osteoplastic 



