SOMATIC 

 MESODERM 



NEPHROTOME 

 SPLANCHNIC 

 MESODERM 



DERMATOME 

 MYOTOME 



MESONEPHRIC DUCT 



NEPHROTOME 



MUSCLE 

 (MYOTOME) 



EPIDERMIS 



CORIUM 

 (DERMATOME) 



MUSCLE 

 (MYOTOME 



SPINE OF NEURAL ARCH 



TRANSVERSE 

 PROCESS 



-CARTILAGE 

 SCLEROTOME] 



"RUM 



NOTOCHORD 



Fig. 116. Top: A cross section of an early chick embryo, showing the three 

 main divisions of the mesoderm — the somite, the nephrotome, and the lateral 

 mesoderm. Center: A later stage in development. The somite shows a segregation 

 into three groups of cells. A loose aggregation cf cells, the sclerotome, migrates 

 around the nerve tube and notochord. The remainder of the somite splits into 

 two layers. The outer layer is dermatome; the inner layer is myotome. In the 

 nephrotome a mesonephric duct has formed and the remainder remains undif- 

 ferentiated in posterior regions. Bottom: A still later stage, showing the sclero- 

 tome differentiated into cartilage around the notochord and spinal cord and 

 assuming the form of a vertebra. The myotome has differentiated into the muscles 

 of the back and the dermatome into the corium, or the mesodermal component 

 of the skin. 



