The mesoderm is the middle germ layer.   Among its many derivatives are the vertebrae and skeletal muscles from somites; the heart, blood, and blood vessels from the lateral plate mesoderm; and the reproductive and excretory organs from the intermediate mesoderm. 

Notochord Notochord Cardiovascular System Cardiovascular System Somites Somites Reproductive & Excretory Reproductive & Excretory
Limb Formation Limb Formation Muscle Muscle Skeleton Skeleton