( 228 ) 



decussations of Monakow and Held, and not in the ventral layers 

 of the corpus trapezoides. 



This opinion, put forward long ago by von Monakow 1 ) in opposi- 

 tion to the now generally accepted opinion of the school of Flechsig 

 which presumes the course of the auditory fibres to be lying in the 

 ventral systems of the corpus trapezoides, has been upheld by the 

 speaker also once before. ") 



The preparations from the deaf-born cat moreover enable us to 

 find an answer to the question how this remarkable degeneration 

 may be occasioned by a pathological process. 



As is well-known, the roof of the 4 th ventricle expands laterally 

 into a so-called recessus lateralis, by which passes the tela chorioidea 

 and consequently this latter is lying free at the ventral border of 

 the oblongata. 



At the entrance of this recessus, medial from the tuberculum 

 acusticum (which forms the medial boundary of the recessus), the 

 stria acustica is situated directly under the ependyme of the ventricle 

 free at the surface. 



Each hydrops ventriculi, tending towards dilatation of the recessus 

 lateralis, becomes a danger for its surroundings, which may be 

 oppressed either from the recessus lateralis as from the ventricle. It 

 threatens to destroy successively first the stria acustica, next the 

 tuberculum acusticum, and only after this latter the lateral root 

 fibres become exposed. Now hydrops ventriculi may be caused by 

 many different morbid processes, both of meningitis, ascending along 

 the tela, and of encephalitis, complicated with ependymitis. 



Now in this deaf-born cat we find hydrops ventriculi with a very 

 important distention of the recessus lateralis, the tela chorioidea is 

 thickened, with neo-formation of bloodvessels. The distention of 

 the ventricle and that of its recessus undermined the lateral wall of 

 the oblongata and the stria was pinched off. (This distention is 

 demonstrated by the speaker on preparations and microphotograms). 

 Similar dilatations of the recessus with the tumefaction of the tela 

 accompanying them, were found also in the IV th ventricle of deaf- 

 and-dumb persons, together with atrophy of the stria acustica. The 

 lateral root-fibres however were not always intact in such cases. 

 They were sometimes destroyed, sometimes not. These facts will soon 

 be published by Mr. A. Brouwer in his dissertation. 



1 ) Monakow, 1. c. 



2 ) G. Winkler. The central course of the N. Octavus. Proceedings of the Royal 

 Acad, of Sciences. 1907. 



