( 227 ) 



in the deaf-born eat does not attain to l / 4 of the compass that fascicle 

 presents in the series taken for comparison. 



The fibres originating in this fascicle and decussating in the raphe 

 (the vigorous decussation of von Monakow) are nearly all wanting. 

 Monakow's decussation is represented barely by a few small fibres. 



Likewise the fibres of Held and their decussation are almost entirely 

 wanting. On the other hand, the ventral secondary octav us- tract in 

 the ventral layers of the corpus trapezoides is represented by a 

 vigorous layer of fibres decussating in the raphe. 



Together with the loss of Monakow's decussation the area at the 

 dorsal and frontal top of the superior olivary bodies, where the 

 fibres of Monakow's and Held's crossings meet, is only represented 

 by a few transverse sectioned fibres. It is wanting, and this deficiency 

 in its turn is accompanied by a very important atrophy of the 

 lateral lemniscus, more especially of its medial bundle of fibres. (The 

 preparations and microphotograms illustrating this, are exhibited by 

 the speaker). 



Apparently nature did achieve in this cat, by some morbid process, 

 a similar experiment as was made long ago by von Monakow l ), 

 when he was the first who succeeded in isolating the dorsal octavus- 

 tract by sectioning the lateral lemniscus. 



For if the lateral lemniscus is sectioned, this so-called Monakow's 

 decussation atrophies rather completely and the stria acustica is 

 reduced to a small rest, whilst the large cells in the opposite tuber- 

 culum acusticum have nearly all disappeared and a certain number 

 of cells are atrophied as well in the nucleus ventralis as in the 

 portio interna corporis restiformis and in the nucleus of Deiters. 

 (The experimental loss and atrophy of those cells is demonstrated 

 by means of preparations and microphotograms of brain-sections taken 

 from rabbits, on which the section of the lemniscus had been per- 

 formed directly after birth). 



In the deaf-born cat almost all the large cells in the tuberculum 

 acusticum have disappeared on both sides (and here — not in the 

 loss of fibres — lies the cause of the slight decrease of the primary 

 nuclei) whilst those in the dorsal portion of the nucleus ventralis, 

 in the portio interna of the corpus restiforme and in the nucleus of 

 Deiters are partly atrophied. 



This case therefore supplies a new argument in favour of the 

 opinion that the secondary system of true auditory nerve-fibres ure 

 to be sought for in the dorsal and intermediate octavus-tracts, in the. 



l ) C. von Monakow. Striae acusticue und untere Sclileife. Archiv für Psychiatrie 

 1891. Bd. XXII. S. 1. 



