is raised in the form of a shield (the future embryo) , and 

 the periphery forms what is called the fetal zone. The 

 shield elongates at straight angle to the egg axis, outlining 

 the axis of the embryo along which forms the primary zone. 



As a result of the fusion or closure of the embryonic 

 layers, they are converted into tubes. The beginning of this 

 process Baer described as follows. Along both sides of the 

 primary zone two unremarkable thickenings arise which appear 

 as a line of dark small balls. This line, the spinal cord, 

 forms the middle part of the trunk. The lateral thickenings, 

 the spinal plates (Laminae dorsalis) , contain only the skin 

 and muscular layers. They correspond to what Pander had 

 called primary folds (plicae primitivae) and what Burdach had 

 called "mirror plates." The crests of the spinal plates 

 deviate from each other and accrete, forming the back of the 

 embryo. The internally folded part of the skin layer is 

 separated from the muscular layer, and quickly thickens to 

 form the central part of the nervous system as a somewhat 

 laterally compressed neural tube. Soon after the formation 

 of the spinal folds, curving of the wide abdominal folds or 

 the abdominal plates (Laminae ventrales) begins downwards. 

 Wolff had called them Fasciae abdominales, because he assumed 

 that they do not reach the posterior part of the body. 



This process is concluded along both sides of the spinal 

 cord where, in the vascular layer, two thickened bands form; 

 their external borders incline to each other and accrete. 

 The mucous layer in the region of the cord separates from 

 it, so that the bands of the vascular layer, called the 

 mesenteric plates (laminae mesentericae) , appear in that 

 free space between the cord and mucous layer. The place of 

 fusion of the mesenteric plates Baer, like Wolff, called 

 the suture of the false amnion. Soon after the formation of 

 the suture, along the sides two other bands separate from it, 

 composed from vascular and mucous layers. They thicken, 

 acquire the form of plates, incline to each other and accrete; 

 hence each intestinal plate (lamina intestinalis) represents 

 a half -canal, and they together form the intestinal tube. 

 The fusion of the intestinal plates downwards represents a 

 simultaneous separation of the embryo from the blastoderm. 



A double conversion of the plates into tubes leads to 

 the formation of the primary organs of the embryo. In all 



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