430 A2fAT0MICAL TBCHNOLOOT. 



Then let it rest upon its ventral side, and grasp it in the cotton, 

 firmly yet gently. Grasp with the forceps the fold of pia which 

 occupies any one of the fissures, especially at the point of forking 

 or junction with another fissure, and pull along the line of the 

 fissure. Usually the fold of pia will come out easily, and with it 

 will be removed some of the pia covering the free surface of the gyri 

 between it and the adjoining fissures. 



Proceed thus until the pia has been removed from the dorsal 

 and lateral aspects of the hemispheres. Avoid pulling across the 

 line of the fissures. The larger forceps are easier to work with, and 

 less apt to puncture the brain ; but the fine forceps are sometimes 

 required for the removal of the pia from the bottom of a deep fissure. 

 The caudal surface of the hemispheres may be reached by slightly 

 veutriducting the cerebellum. The mesal pia can be removed only 

 at the margins of the hemispheres. 



On one side, preferably that on which the If. opticus was cut 

 shorter, raise the mass of nerves formed by the divisions of the iViV". 

 trigeminus and abducens by its lateral border, and cut with the 

 scissors the N. oculomotorius which holds the mesal border close to 

 the brain. This will permit the mass to be turned caudad so as to 

 expose the course of the slender N. trochlearis which emerges from 

 between the hemispheres and the cerebellum. It also permits the 

 removal of the pia from the region just laterad of the hypophysis. 

 Grasp the pia on the ventrimeson just caudad of the Lohi ol., and 

 pull caudad so as to remove it as far as the chiasma, taking care 

 not to tear the delicate terma just dorsad of the chiasma. Then 

 remove the pia from the olfactory tracts. 



In removing the pia from the metencephalon, the position of the 

 nerve roots should be constantly kept in mind, the tripod (Fig. 26) 

 should be frequently ased, and traction should be avoided. It is very 

 difficult to preserve the delicate funiculi of the N. Tiypoglossus, for 

 their connection with the pia seems to be closer than with the brain. 

 Sometimes it may be necessary to submerge the brain in water or alco- 

 hol, so as to float the roots out and render them more apparent. In 

 some cases it is safer to cut carefully about the point of passage of the 

 root through the pia, leaving a bit of the membrane attached thereto. 



As suggested on a previous page, it is often as well to leave the 

 roots longer on one side than the other, but the choice may be 

 determined mainly by the degree of success in the various opera- 

 tions which have been described. 



