14 



C. WINKLER. THE CENTRAL COURSE 



lamina of bone, constituting the promontory and covering the 

 cochlea. 



If the promontory be opened by means of the chisel, this instru- 

 ment, that ought to be exceedingly sharp, is put on along this 

 line, i. e. along the lateral and posterior border of the pyramid, 

 and with a single, soft blow of the hammer the lamina of bone, 

 covering the cochlea, is sectioned. 



Next the chisel is put on along the most anterior nervnre of 

 the pyramid (partly along the border of the bony hole enclosing 

 the m. stapedius), and the thin lamina of bone is sectioned again. 



Fig. 5. 



The bulla ossea is opened. The aditus ad tubam Euslachii, the promontorium, 

 the foramen rotundum, the foramen 'ovale are seen. 



A N. cerv. II, B N. cerv. I, C N. Vagus, D for. rotnndum, E N. symp., F N. hypogl., 

 G promont., H N. lar. sup. , I tuba' Eustachi, J for. ovale. 



By a third stroke of the chisel both diverging lines of section 

 are united straight before the foramen rotundum. 



A very narrow lamina of bone, lying before it, remains uninjured. 



The thin lamina of bone covering the cochlea is now detached, 

 and may be removed with a pincet or an excavator. 



If one does not dare to open the promontory with the chisel 

 for there is some danger that the thin lamina, covering the 



