302 



HISTOGENESIS 



cells from the ventral portion of the myotomes has been recorded by various 

 observers, recently by Ingalls. These cells soon lose their epithelial character 

 and blend with the undifferentiated mesenchyma of the limb buds (Fig. 291). 

 From this diffuse tissue then the limb muscles are differentiated, the proximal 

 muscles being the first to appear. 



FIG. 290. Reconstruction of a 9 mm. embryo to show the myotomes (Bardeen and Lewis). 



The musculature of the head is derived from the pre-otic mesenchymal 

 tissue which condenses to form premuscle masses. No myotomes are developed 

 in this region. 



The pharyngeal muscles probably arise from the mesenchymal tissue of the 

 third branchial arch. 



