This chapter discusses the difference between the two types of osteogenesis. These are: intramembranous ossification and endochondral ossification. Both types begin with mesenchymal cells, which are usually of mesodermal origin. The initiation of intramembranous ossification occurs when specific mesenchymal cells called osteoblasts begin to secrete a specific extracellular matrix. The chapter explains the origin of bone marrow, the development of somites, including the origin of the vertebrae, intervertebral discs, and the nucleus pulposus of the discs. It explores the development of the skull, and explores the origins of myotomes and lateral mesoderm and their contributions to muscle development. The chapter aims to compare the three major types of muscles in the human body, their origins, and their differentiation. These are: skeletal muscle, cardiac muscle, and smooth muscle. Our arms and legs are powered by skeletal muscle, our stomachs and bladders are able to contract because of smooth muscle, and our blood is pumped by the cardiac muscle of the heart.