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After studying this chapter, you should be able to:

  • Describe the two mechanisms by which bones form, and indicate which bones develop via each mechanism.

  • Describe the origins and development of each division of the skull.

  • Trace the development of the vertebrae, sacrum, coccyx, and ribs from the sclerotome of somites, as well as the development of the sternum from the parietal mesoderm.

  • Compare and contrast skeletal development and organization in the upper and lower limbs.


  • Bones develop from mesenchyme (embryonic connective tissue, derived usually from mesoderm and sometimes from the neural crest).

  • Bone formation occurs via two mechanisms:

    • Intramembranous ossification

      • Mesenchyme cells give rise to osteoblasts, which build the bone.

      • Intramembranous ossification is mainly used in the formation of flat bones (especially those of the skull) and most of the bones of the face.

    • Endochondral ossification

      • Mesenchyme cells give rise to chondroblasts, which construct a miniature hyaline cartilage model of the bone (Figure 2-1A).

      • The cartilage is later replaced with bone.

      • In long bones, this process begins at the primary ossification center, located in the diaphysis (shaft) (Figure 2-1B).

        • Blood vessels enter the primary ossification center and bring in osteoblasts, which produce bone matrix.

        • The ossification front progresses, radiating outward from the primary ossification center through the cartilage model.

      • Secondary ossification centers form at the epiphyses around the time of birth as blood vessels enter these sites (Figure 2-1C).

    • Most bones in the human skeleton develop via endochondral ossification.

  • Although ossification begins during embryonic development, it continues for the first few decades of postnatal life. Different bones complete their ossification at different times.

Figure 2-1.

Endochondral ossification. (A) A miniature model of the bone is formed from cartilage. (B) This model is replaced with bone, beginning at the primary ossification center in the middle of the diaphysis, where blood vessels enter and bring in osteoblasts. (C) Ossification progresses from the primary ossification center. Blood vessels enter the epiphyses and form secondary ossification centers there.

Source: Reproduced, with permission, from Anthony L. Mescher. Chapter 8, Bone. Junqueira's Basic Histology Text and Atlas, 16e. McGraw Hill. 2021.


  • Most components of the axial skeleton are derived from the sclerotome portion of somites (from the paraxial mesoderm), with some exceptions that are derived from the parietal mesoderm (from the lateral plate mesoderm) and neural crest cells (from the ectoderm) (Table 2-1).

Table 2-1.Embryonic origins and ossification mechanisms of the components of the axial and appendicular skeleton

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