428 



EMBRYOLOGY. 



days) faint, regular infoldings of its lateral walls, by means of which 

 it becomes separated into several smaller parts, lying one behind the 

 other. Inasmuch as these afterward disappear without leaving any 

 trace, no great importance was ascribed to them by the earlier 

 investigators (REMAK). Recently, however, several persons have 

 maintained for them a real significance. RABL and BERANECK 



cmg 



kh 



Fig. 241. Brain of a human embryo from the first half of the fifth month, divided in the median 

 plane ; view of the median surface of the right half, after M.HALKOVICS. Natural size. 



rn, Olfactory nerve ; tr, infundibulum of the between-brain ; ana, commissura anterior; ML, 

 foramen of MONRO ; frx, fornix ; apt, septum pellucidum ; bal, corpus callosum, which 

 be'.ow, at the germ, is continuous with the embryonic lamina terminalis ; cmg, sulcus calloso- 

 marginalis ; fo, fissura occipitalis ; zw, cuneus ; fc, fissura calcarina ; z, epiphysis ; vh, corpora 

 quadrigemina ; kh, cerebellum. 



msp 



Fig. 242. Brain of a human embryo from the second half of the third month, seen from behind, 



after MIHALKOVICS. Natural size. 

 msp, Longitudinal (interjMillial) fissure; vh, corpora quadrigemiua ; vma, velum medullare 



anterius; kh, hemispheres of the cerebellum; v*, fourth ventricle (fossa rhomboidalis) ; 



</">, medulla oblongata. 



recognise in them a segmentation of the brain-tube which is related 

 to the exit of certain cranial nerves and is of importance in regard 

 to the question of the metamerism of the entire head-region. The 

 circumstance that the folds are so transitory appears to me to favor 

 the older view. 



In the further development of the vesicle of the after-brain a 

 distinction arises between the floor and side walls on the one hand 



