mi: OBfi OM * 





MI!.- iiu-iitly 1) num. still uioro sharply mark. .1 

 oil' from ono another, owim; U> th. alt ration ..f ti 



rf yt> nh 



Fig. 235 Brain of a human embryo of the third week ( /. , After Hia. 



;//(, C- ; 'o; kh, nh, vesicle - 



lluin and niril ilia <>l>!c >n'gatu ; au, optic vesicle ; gb, auditory vesicle ; tr, infimdibulum ; 

 r/, area rhi:. . inu-hal flexure ; kb, cephalic l!- 



At the beginning tin- tlm-,- brain-ve l>y tin- 



i-ictions lie in a straight line one behind the other (fig. 87) 

 ;il'(>\*' thi- chorda dorsal is ; the la> 'K 



only as far as to the anterior end of the mid- 

 lirain vesii-le. where it tajn-rs to a point. But 

 from the moment when the oj>tic M >icle> 

 to le constricted otV. tin- three primary v- 

 shift thfir positions in siu-h a \vav that the 

 longitudinal axi^ uniting them underlies >har|>. 



characteristic folds, which are distinguished as 

 the cephalic, pntn1. and nurfmJ tlrxnns (fig. 

 235 M, nb). 



Tin- i-ause of the formation of tin- curvatui-es, 

 which are of fundamental inij'ortamv in the 

 anatomy of the brain, is to be sought princi- 

 pally in the more vigorous longitudinal powth 

 which dUtin.irni.-hi- the cerebral tube, and more 

 especially its dorsal wall, from the surroundini: 

 parts. A- His has established by me;i 

 measurements, the fundaim-nt of t!.- brain moiv 

 than doubles its length, while tin- >pinal 

 increase> l>y only about one-sixth of it> length. 



The cejthaft'r fluswn (tig. '2:^ IJ>) is developed first. The floor of 

 the fore-brain sinks downward a little around the anterior end of the 

 chorda dorsalis (tig. 'I'M cli). and forms ( right angle with 



236. - Brain of a 

 human embryo seven 

 weeks old, parietal 

 (Scheitel) aspect, after 

 M 11 M.KDVICS. 



or in- 



llial fissure (Man- 



telspalte), at the bottom 



of which is seen the 



lamina ter- 



minalis(Schlaasplatte); 

 hemisphere ; 

 th, betwoen-brain 

 miil-bniin ; hh, hiiid- 

 n and after-brain. 



