OF THE NERVUS OCTAVUS. 17 



c. The sectioning of the corpus trapezoides. 



Cochlea , vestibulum with ampullae having been removed and 

 the trunk of the N. octavus lying before us, it is very easy , guided 

 along by this trunk , to divide with a lanciform knife the dura 

 mater and to damage the medulla oblongata. 



This lesion of the medulla oblongata is produced invariably dor- 

 sal from the ramus spinalis N. V, and if due care be taken that 

 the knife does not penetrate too far, the corpus trapezoides is cut 

 from the nucleus ventralis N. VIII, without many complications. 

 The knife enters the oblongata at the origin of the N. VIII , cuts 

 generally the dorsal part of the ramus spinalis N. V. , is intro- 

 duced between it and the oval area of the corpus restiforme in 

 the so-called interior part of this latter, and terminates more or 

 less far dorsalward in this interior part (the corpus juxta-restiforme). 



The destruction caused by the knife may be controlled post 

 mortem when the medulla oblongata is examined in serial sections. 



By this section the corpus trapezoides, at least in its distal 

 portion is divided from the nucleus ventralis N. VII 1 dorsal (lateral) 

 from the ramus spinalis N. V. 



There is still another manner of sectioning the corpus trapezoides , 

 without destroying the peripherical organs of the N. VIII and the 

 octavus-roots. The bulla ossea having been opened , the promon- 

 tory is left undamaged, but medio-ventral from the promontory, 

 passing through the cavity (or next to it) that contains the M. stape- 

 rius (this latter being removed if necessary) , the posterior wall of 

 the bulla is punctured , and the glossy N. trigerninus does appear. 

 Directing the knife by the aid of this nerve, the dura mater is 

 cleft and the medulla oblongata is damaged, i.e. the corpus trape- 

 zoides medial from the ramus spinalis N. V. This lesion however 

 is of less importance than the former operation. 



d. The section at the dorsal octavus-tract. (VON MONAKOW'S stria 

 medullaris). 



Next to the operations at the peripherical organs of the eighth 

 cerebral nerve and to the section of the ventral systems of the 

 root-fibres of this nerve, it may offer great importance to section 

 their dorsal systems. 



The section of the dorsal octavus-tracts , simple though it may 

 be, must be attempted from the fourth ventricle. In operating on 

 rabbits, under strict asepsis, it does not offer any great difficulty 

 to lay bare in the mid-dorsal line the membrana atlantico-occipi- 

 talis, without any haemorrhage. This membrane being cleft , a view 



Verhand. der Kon. Akad. v. Wetensch. (Tweede Sectie.) Dl. XIV. 



