( 23 ) 



from an anthropomorphic point of view), thus forming a vertically 

 distended slit, on the transverse section, it possesses only on its dorso- 

 lateral wall any tibre layer on the "substance subcpcndymare" to 

 which the name of callosal tapetum might be given. 



From this point the fibres — such as have not already turned 

 dorsally — proceed latei-ally. Itmay clearly be deduced therefore that, 

 especially in the occipital region, cell changes etc. will be found 

 after cutting of the corpus callosnm, chiefly or solely in the dorsal 

 (medial and lateral) jiortions of the cortex. The fact that I took my 

 exam[)les exclusively from these convolutions or tracts is due to the 

 circnmstance that the secondary abnormalities in the ventral cortical 

 regions could not be shown at all, or with any degree of clearness. 



The degeneration in the fivihrla cannot be seen in the Pal- 

 preparations. This must be ascribed partly to the fact that the 

 psalterium fibres, some of which must of course be degenerated 

 in a normdl state, are but slightly meduUated. Their lesion is visible 

 in VAN GiESON preparations by the too diffuse reddish colour of the 

 fimbria. 



If we consider the results from a more general point of view we 

 must first bear in mind the fact that in all mammals three commissural 

 systems in principle commnnicate between the two hemispheres of 

 the cerebi'um. Adopting the nomenclature introduced by Edinger 

 and Elliot Smith, continued and extended by Ariens Kappers^), 

 we can distinguish fibres running between the two secondary 

 olfactory regions (the palaeo pallia) : the pars olfactoria commits? trae 

 tnitcrioris; fibres running between the two tertiary olfactory regions 

 (the archipallia i.e. the amnion's formations): the psalterium; emd 

 fibres between the two cortices cerebri after deducting the above- 

 mentioned regions (the neopalUa i.e. which in the majority of the 

 mammals is the larger part of the covering of the brain) : pars 

 temporalis comiii. ant. and corp. callosnm. The archicommissura 

 and the callosal part of the neocommissura have been examined by 

 my experiments. 



Both are shown to originate in cells beneath the iimer granular 

 layer if Kapper's (1. c.) theory, derived from lower animals (reptiles) 

 on the evolution of the Amnion's formation be accepted. 



These two commissura systems, moreover, have the same horizontal 

 localisation for their place of origin as the projection systems examined 

 in this respect, but originate as far as concerns the callosum, either 



1) Ariens Kappers und Theunissen, Die Phylogenese das Rhinencephalons etc. 

 Folia Neuiobiologica, Bd. I. 



