( 338 ) 



Kiiijillv wo iiKMilioii ;is s(M('-('\ idoiit llial iii cxacllv iikmH.-iI seclioiis 

 all llic just ineiitioucd hordoi-s, urooxcs and prominciicos ai'c almost 

 entirely lacking. 



Sagittal sections I'lii'tlier |»ro\o conccniing the n)id-i)rain that at 

 this sta2:e it covers the islhniiis to a i-clati\elv small extxMit, less e. g. 

 than in a hnman embrvo of '1 to 3 months. The cerebellum shows 

 in sagittal sections still a horn-shaped form. Of the occipitally directed 

 ridge, which is so characteristic for man, nothing is to be found yet. 



The oldest of the embryos at my disposal had been dissected into 

 a somewhat slanting frontal series. Here also nothing can be detected 

 of a crus epirliinicum corporis striati. Notable is the considerable 

 thickening of the wall in I he basal portion of the medial ventricular 

 wall. It oidy becomes distinct after the lateral ventricle and the 

 ventricle of the olfactory lobe have already coalesced for some time 'j. 

 The thickened low^er poi'tion and the not-thickened upper portion of 

 the wall are sej)ai'ated on the inner surface of the ventricle by a 

 very distinct groove which can be followed almost as far as the 

 frontal plane of the terminal lamina. It has nothing to do with the 

 marking olf of the olfactory lobe, as it appears considerably latei- 

 and also lies somewhat higher than the iissni'a rhinalis latei-alis. In 

 the same way it is entirely independent of the amnion fold, sinc(> 

 it lies considei'ably lower than this lattei'. Microscopically it forms 

 a pretty sliai'p basal limit for the ])allium formation. Therefore I 

 designate it as margo pallii medialis ijdernus (v. also below). In 

 the section where the third \'enlricle is \ isible for the first time, it 

 appears as a paired strnctnre ; between the two terminal |)oints of 

 the \entri('le a median grooxe incises into the xcnlricnlar roof 

 (cf. above). 



Special notice deserves the lloor of the thii'd veidi'icle. Its median 

 grooN'e forms a very sharp incision. 'J'he lateral pai'is of the lloor 

 rise, so to say. in three gradations. The most latei*al prominence 



groove, the m a r g o I \\ 1) e r c. u 11 o 1 f a c t o r i i. '\ lii s ^- r o o v o als o 

 is generally not so d i s I i n c t I y \\ e i- c e j) t i 1) I e a t I li e in v dial 

 e (1 g e, on I li e o I li e r li a n d a I I li e lateral a n d a n t e r i o r e d g e s 

 it is well (] e v e I o p e d a n d li e n c e li as li c r e o f t e n h c o n d e s i g- 

 n a t e (1 a s 1' i s s u r a r li i n a 1 i s medialis s. o n I o ]■ li i n a I i s. At I li c 

 )) o s t e r i () r edge, I o \v a )• d s I lie s u b s t a ii I i a pei-roiala anierior, 

 it i s g e n e r a 1 1 y r a t li c i' s li a ! I o w. W' li e n t li e c a ]^ p a o 1 I', r e a rdi e s 

 f a r I) a c k \v a r d, t li e a n t e !■ i o r m a r g o I n h. o If. c di n e i d e s 

 e n t i r e 1 y o r p a r 11 y \v i I li i he ni a r g o c a p p a <■ «i 1 I'. 



1) In what follows llie series is supposed lo be examined from before backward. 



