Initially, the thin sheath of mesodermal layer proliferates and forms the paraxial mesoderm medially and lateral plate laterally. They are connected by the intermediate mesoderm. The lateral plate divides into two layers: somatic (parietal) and splanchnic (visceral) mesoderm. The paraxial mesoderm breaks into segmented blocks, the somites (42-44 pairs).
The epithelial cells forming the somites lose their epithelial shape and migrate in the direction of the notochord and the spinal cord to form the sclerotome (future vertebral column). The dorsal wall of the somite differentiate into the myotome (furute muscles) and the dermatome (future dermis).
The intermediate mesoderm forms nephrotomes cranially and nephrogenic cord caudally, both developing into the excretory units of kidneys, gonads, ducts and accessory glands.

Derivatives of the mesoderm - day 17

Derivatives of the mesoderm - day 21

1 . Amniotic cavity
2 . Mesoderm
3 . Notochord
4 . Ectoderm
5 . Endoderm






1. Intermediate mesoderm
2. Endoderm
3. Splanchnic mesoderm
4. Somite
5. Somatic mesoderm
6. Surface ectoderm
7. Neural tube
8. Dorsal aorta
9. Notochord
10. Yolk sac
11. Intraembryonic coelom

Parietal and visceral mesoderm layers line the intraembryonic coelom. The parietal mesoderm participates in the formation of the lateral and ventral body wall, while the visceral mesoderm participates in the formation of the gut. They also form the mesothelial lining of the serous membranes.

Differentiation of the somite

Differentiation of the somite

1. Neural groove
2. Notochord
3. Somite
4. Ventral somite wall
5. Surface ectoderm
6. Intermediate mesoderm
7. Endoderm
8. Lateral plate




1. Myotome
2. Dermatome
3. Sclerotome
4. Surface ectoderm
5. Endoderm
6. Neural tube
7. Dorsal aorta
8. Notochord