. (12 ) 



Anatomy. — " The origin of the fibres of the corpus callosum and 

 the psalterium." By Dr. C. T. van Valkenburg. (Communicated 

 by Prof. L. Bolk). 



(Communicated in the meeting of March 25, 1911). 



Embryology, histology and pathological anatomy have not yet 

 succeeded in fixing beyond all doubt the origin and the ending of 

 the callosal fibres in the cortex cerebri. The communications on this 

 subject show somewhat different results. 



The earlier interpretation of the c. callosum as a typical commis- 

 sure between the hemispheres has been rendered improbable, at 

 least for man, by the anatomical researches which showed asymmetrical 

 secondary degeneration in both hemispheres after callosal lesions. 



In well-stained [jreparations it is possible to point out degenerated 

 callosum fibres through some of the deepest cortex layers ; sometimes 

 such elements are isolated by the degeneration of the surrounding 

 fibres and may be traced in the same way. But neither experimental 

 nor pathological preparations enabled me to conclude with suflicient 

 certainty which of tiie cortex layers might give origin to or receive 

 callosal radiations. 



The great difficulty in every case is the absence of myeline sheaths 

 in the last ramilications, viz. in the axoiies near their origin, the 

 usual methods depending upon the demonstration of myeline alterations 

 (Weigert, Marchi). By means of the GoLGi-method Cajal ') showed 

 the probability that in the smaller mammals (newborn rat, rabbit) 

 pyramidal cells of difierent size may send their neurones between 

 the constituents of the corpus callosum, whereas from other cortex 

 cells axis-cylinders may originate which give collaterals into the same 

 system. Kölliker '), who confirmed these opinions, found in the 

 mouse axones arising from polymorphic cortex cells, bifurcate in the 

 area of the callosum fibres : one of the branches remains in the same 

 hemisphere (associative fibres after Kölliker), the other passes into 

 the collateral one. 



The impossibility of tracing in a histological preparation the whole 

 traject of any longer nerve fibre compelled me to have recourse to 

 experiments. 



It is well known that the regressive (even temporary) alterations 

 in the nerve cells after cutting their axones, depend upon many 

 factors. The distance of the lesion from the cell and the presence of 



1) Cajal: Textura del sist. nervioso. Tomo II. Parte 2. Pag. 145 seqq. 



2) Kölliker: Handbuch der Gewebelehre. Band II. S. 664 flgg. 



