150 



be seen, wliicli liave been distinguished by His as liie cms epirhi- 

 jiicum and the crus mesorhinicum '). 



Both crura are separated by a fissure wliioli until now has been 

 named /issura intercruraU.i, but whicli may be called /iss. neo- 

 pnlaeostrhitica since my researches have convinced me that the 

 mesial crus is the primordiiim of tiie palaeostriatnm whereas the 

 lateral cms is the primordium of the neostriatum. 



Fig. 16. Transverse sectiou of the forebrain of a human foetus of 27 m.M. 

 total length. This section being slightly oblique, the right side shows 

 a more frontal level than the left one. 



The mesial crus does not e.xtend as far frontally as the lateral 

 one, as the figure — on the right side — shows, where the mesial 

 crus or palaeostriatnm ') has already disappeared, the neostriatum 



1) His called the caudo-medial edge of the latter cms metarhinicum, but it is 

 belter not to distinguish this as a separate part since it is njerely the caudo- 

 medial side of the raesorhinic crus. It is better to speak only of a lateral and 

 medial primoria as also Hochstetteb and Miss HijNes do. 



') 1 may mention here that in this embryo of 27 niM. the transitory cavities 

 of the corpus striatum, which Essick first described (Carnegie embryologie public. 

 No. 222), as being constant in human embryos from 15 — 20 mM, and less con- 

 stant up to 24 mM, wei-e still present. They are confined in my material to the 

 palaeostriatuni. I quite agree with Essick that they may be due to insufficient 

 drainage of the brain in that stage in which the production of metabolic solutions 

 may surpass the possibility of drainage, the more so since phylogenetically as 

 well as ontogenetically the dual source of production of liquor (choroid plexusses and 

 ependyma on one hand and intra cerebral vessels on the other) is established 



