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the skeleton will form itself, and willi Amniotes a rather considerable 

 part of it is used. This mesenehym accumulates between tlie chorda 

 and the medial lamella of (he pi-imordial vertebra, so that the 

 primordial vertebrae are pushed in a lateral direction from the 

 chorda. The intervals between the different primordial segments are 

 distinctly indicated I)}' the transversal course of the inlersegmental- 

 or interprotovertebral vessels. 



What is now v. Ebnkk's discovery? 



This that from the lumen of the primordial vertebra a narrow 

 fissure runs in a medial direction to quite near the chorda. This 

 fissure, called by v. Ebnkr intervei'tehral-fissnre divides each segment 

 into a cleai'ly defined anterior and a posterior (cranial and caudal) 

 half. With Tropidonotns natrix (npou which v. Ebner made his first 

 investigations) this fissure is most distinct in the neighbourhood of 

 the spinalganglions. More dorsally it disappears; ventrally it can 

 easily be followed as far as the region of the chorda. As was said 

 this fissure was first observed by v. Ebnek in Tropidonotns natrix 

 and afterwards it was shown by the same investigator in hens, 

 mice and hats. This discoveiT was soon confirmed by other investi- 

 gators with other animals and also with man. The existence of the 

 fissure is no longer contested. Van Ebnek could also already show 

 that the intervertebral fissures agreed completely with the joints of 

 the later permanent vertebrae. According to him they disappear in 

 the end in the dense mass of tissue, in which afterwards the articular 

 cavities between the vertebrae occur. 



The permanent vertebrae come now into existence each in the 

 region that is limited between 2 intervertebral-fissures. Consequently 

 each vertebra belongs to two segments and is constructed of the 

 caudal half of a discretional segment and the cranial half of the 

 next following one. This agrees consequently entirely with Remak's 

 assertion cited above, with this difference however, that the inter- 

 vertebral-fissures that indicate the intervals between the permanent 

 vertebrae, can already be observed when the intervals between the 

 segments have not yet disappeared, so that (he unsegmented blastema, 

 which, according to Remak, should exist for some time, does in reality 

 not occur. 



After this explanation it is obvious what must be understood by 

 re-segnieulation of the vertebral column. The segmentation that is 

 expressed by the permanent vertebrae, is different from that which 

 is given by the primordial vertebrae; a new and another segmen- 

 tation has taken place. 



How do now the fused caudal and cranial segments behave in 



