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Bones arise from three distinct lineages. The somites generate the axial skeleton, the lateral plate mesoderm generates the limb skeleton, and the cranial neural crest gives rise to the branchial arch and craniofacial bones and cartilage. The embryonic “skeleton” is at first composed of mesenchyme. These become the sites where ossification takes place in a process termed osteogenesis that occurs by one of two pathways: intramembranous ossification (bone forms directly within preexisting mesenchymal tissue, which is arranged in sheetlike layers that resemble membranes) or endochondral ossification (bone forms within hyaline cartilage that develops from mesenchyme). Intramembranous ossification occurs primarily in the bones of the skull. Other bones form by endochondral ossification.
The bones of the body are collectively known as the skeleton and serve as the structural framework for the body which supports soft tissues and provides attachment points for the tendons of most skeletal muscles. The skeleton protects internal organs, facilitates movement via tendon-muscle attachments and serves as a storage site for minerals (for example 99% of total body calcium is stored in the bones). The bones also contain red bone marrow (blood cell production) and yellow bone marrow (triglyceride storage).