The intermediate mesoblast
The intermediate mesoblast (stage 10) is found between the paraxial mesoblast and the lateral plate mesoblast. This longitudinal, dorsally lying crest is called the urogenital crest and serves as the origin of the kidney and gonads. It forms cell masses in the neck and upper breast regions that exhibit a metamerism: the nephrotomes.
In the more caudally lying regions it remains unsegmented and forms the so-called nephrogenic cord.
The lateral mesoblast
The lateral plate mesoderm is composed of two thick layers that surround a cavity, the intraembryonic coelom (the coelom represents the future serous cavity of the trunk: peritoneal, pleural and pericardiac cavities).
- The somatopleure, which is close to the ectoderm, is involved in the formation of the lateral and ventral walls of the embryo.
- The splanchnopleure, which lies on the endoblast, takes part in the formation of the wall of the digestive tube