( 335 ) 



i'csenii)liu,ii' a laiicc poiiil. Also llic rooi' ol' llir iiicdiaii-inaiillc-slit 

 which was al lirsl Ioi'iikmI hv Ihc l'ohhMl rooi" of tho lliahinuMi- 

 (•ephah)ii, now Uccomcs shar|)lv poiiiliMl. The (issui-a hi|)|UH'aini»i oi- 

 rathei- its h)W(N- lip marks prcllv shai-ply. cvcii aller Ihc scparalioii 

 of the hcinis|>hci'(>s from each olhcr. Ihc poinl rcaclic*! I»v llic for- 

 mation of lh(^ pallium. Il is also vcrv i-cmarkaltlc Ihal N and S' 

 no longer exactly correspond to each other lopo,ura|)liicall\ , lait that 

 ,S" becomes sitnated somewhat \ (Mitrallv of S. Uelow S the medial 

 wall of the frontal Iti-ain shows a second leel»l(> promin(Mice J\ U 

 and the candate nucleus l(>rminale in the mcMlial respecli\ cly lateral 

 wall of the \enli-iculus lohi ollactorii and in doing so g-row snioothei'. 

 After the disa[)pearance of the tissnra hippocampi the medical wall 

 first remains (piite undi\id(Ml in many sections, hut then (almost 

 exactly in the corres|»oiiding place) the medial ttM'ininal part of the 

 rhinal latei-al (issni-e apjieai's as a shallow groove. 



{3. The cavity of the thalamenccphalon shows in its posterioi- pai-ts 

 two grooves, an n])[)er one x, which is continued in the lateral 

 groove of the midbrain ventricle (a(pie<luct) and fVonlally vei-y soon 

 smoothes out, and a lower one -?., which can l)e ti-aced as far as the 

 region of the foramen Monro!. The lattei- on(> is accomi)anie(l during 

 the anterior part of its course by a i)arallel groove n of a slightly 

 more basal situation. Further folds of the surface are temporarily 

 observed within reach of the o[)tic stalks and of the corpora 

 mammillaria. I j-egret not to l)e al)le to decide whether / oi- n has 

 to be interpreted as the sulcus Monroi ; to me it seems more likely 

 that fi deserves this designation. 



'J'he picture is materially comj)leted by studying a sagittal series 

 belonging to about the same stage of (le\(dopment (length of the 

 embryo il mm). 



In a section sitnated soukwn hat laterally of the medial plane, we 

 find as follows : 



The fossa mesodiencephalica is sharply marked. P)efore it and for 

 a smaller part also in it, lies the long-stretched cross-section of the 

 jiosterior commissni-e. A \(^v\ shallow grooxc which I designate by 

 E corresponds approximately lo the b-onlal plane of the (epiphysis. 

 There is no objcclion lo designating with v. Kii'I'I'kh (cf. v. KrpKi'KK 

 in Hkrtwkj's \'er,L'l. I^utw. geschichte p. 95) as synence|)halon the 

 I'oof part between the fossa mesodience|)lialica and A\ 'J1ie fossa 

 ))raediencephalica is not shar|»ly markcMl. It might l>e sought at the 

 ])lace where the iinaginalion of iIk^ plexus chorioideus veidricnli 

 tertii occurs. It must be em|)hasised that il remains doubtful whether 

 this spot corresponds to the velum trajisversum of lower vertebrates. 



