14.1 The origin of muscle tissue

• Genesis of the middle germinal layer (mesoderm)
  
• Differentiation of the mesoderm layer into muscle tissue

Genesis of the middle germinal layer (mesoderm)

With only a few exceptions the musculature stems from mesoblast cells that – for their part – come originally from a population of epiblast cells (ectoderm cells), which immigrate via the primitive streak 6-11 between the hypoblast and the remaining epiblast cells. They thus form a middle germinal layer, the mesoderm layer.

Fig. 1
The left image shows an embryo dorsally. The epiblast cells stream in via the primitive streak and nodes and form the mesoderm layer. In the right image the embryo is shown in a median longitudinal section. The region of the prechordal plate is colored in red. The area where the cardiogenic plate arises is indicated by a red arrow.