EXPOSURE OF THE BRAIN. 425 



Bring the mandible to a right angle with the rest of the head, and 

 divide the soft parts at the angles of the mouth if any remain. In 

 doing this, insert the arthrotome sidewise so that it may pass 

 "between the Pre. coronoideus and the projection left after the 

 removal of the cephalic root of the zygoma. 



Feel for the caudal border of the hard palate and for the tips of 

 the Ossa pterygoidea (Fig. 57) ; at a point midway between push 

 a scissors blade entad of the soft palate, and divide it ; then divide 

 the mucosa forming the dorsal wall of the postnares, and dissect it 

 up as far as the atlas. 



The mandible is now attached to the rest of the head by some 

 muscular fasciculi and by the slender piers of the Tiyoid arch (Fig. 

 30, § 224). These last join the skull at the lateral side of the bullae, 

 where they are to be divided vsdth the arthrotome ; if it be desired 

 to examine the mode of their attachment, they may be cut with the 

 bone scissors at a little distance from the attachment. 



Ventriduct the tip of the mandible still farther, and dissect off 

 the muscles, rectus anticus capitis (§ 628), that are inserted between 

 the bullae ; near the caudal ends of the mesal borders of the bullae 

 emerge several nerves, which should be divided with the scissors or 

 a sharp scalpel at about 1 cm. from the skull. By continuing the 

 removal of the muscles across the Arth. atlodido-occipitale this is 

 exposed. Put the membranes upon the stretch, and divide them 

 with a Charriere scalpel along the cephalic border of the atlas. 

 This exposes the myelon, which is to be divided in the same way. 

 The remaining ligaments and the cervical muscles may be cut with 

 the arthrotome, and the skull proper is then separated from the 

 rest of the body. Place the skull in the normal salt solution, and 

 wash the hands and the instruments which have been used. 



§ 1102. Exposure of the Brain. — In the later stages of the ope- 

 ration there is considerable risk of injuring the brain by the unin- 

 tentional pressure of the nippers. 



In whatever way the bone is grasped, when force is applied, the tendency is to approxi- 

 mate the cutting edges as nearly as possible, and thus to bring their planes into right 

 angles with the surface of the bone. This of course crowds the convexity of the ental 

 blade against the brain, and may crush it seriously. It may occur either from the turn- 

 ing of the nippers in the hand, or more frequently from the escape of the skull from the 

 grasp of the other hand. The accidents may usually be avoided by keeping the danger in 

 mind, by having the right hand dry, and aiding the grasp of the more or less slippery 

 skull by a small towel or bit of coarse muslin ; this last is also desirable during some 

 stages of the operation as a protection of the hand itself from abrasion. 



