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After studying this chapter, you should be able to:

  • Describe the embryonic origins of skeletal, cardiac, and smooth muscle.

  • Describe the development of the skeletal muscle of the head from somitomeres and somite myotomes.

  • Describe the formation and innervation of the epaxial and hypaxial muscles.

  • Relate the process of limb rotation to the arrangement of the flexor and extensor muscles in the upper and lower limbs.


  • There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle.

  • Nearly all muscle is derived from mesoderm.


  • Skeletal muscle is derived from the paraxial mesoderm (Figure 3-1).

  • The paraxial mesoderm segments into bilaterally paired somitomeres, which then condense and organize into somites (except for somitomeres 1–7).

    • In total, 42–44 pairs of somites are formed. After the caudal-most somites disappear, about 35 pairs remain.

  • Each somite gives rise to three parts: dermatome, myotome, and sclerotome.

    • The myotome portion gives rise to skeletal muscle.

Figure 3-1.

Paraxial mesoderm differentiation. (A) A transverse section of the embryo during the third week of development reveals two columns of paraxial mesoderm forming just lateral to the midline. (B) The paraxial mesoderm segments into bilateral pairs of somites, producing raised bumps on the dorsal surface of the embryo. (C) Each somite differentiates into three components, from superficial to deep: dermatome, myotome, and sclerotome. The myotome portion will form skeletal muscle.

Source: A, Reproduced with permission from T.W. Sadler. Langman's Medical Embryology, 14e. Wolters Kluwer; 2019; B, Reproduced, with permission, from F. Gary Cunningham, Kenneth J. Leveno, Jodi S. Dashe, Barbara L. Hoffman, Catherine Y. Spong, Brian M. Casey. Chapter 7: Embryogenesis and Fetal Development. Williams Obstetrics, 26e. McGraw Hill. 2022; C, Reproduced with permission from T.W. Sadler. Langman's Medical Embryology, 14e. Wolters Kluwer; 2019.

Head Musculature

  • Somitomeres 1–7 give rise to most of the voluntary musculature of the head (Figure 3-2).

    • Some somitomeres (1–3 and 5) give rise to the extraocular muscles.

    • Cells from some somitomeres (4, 6, and 7) migrate into the pharyngeal (branchial) arches (see Chapter 9), where they give rise to musculature of the face and pharynx.

      • These muscles are called branchial muscles due to their embryonic origin in the branchial arches.

      • They are innervated by the cranial nerves associated with their respective arches.

  • The intrinsic laryngeal muscles and tongue musculature are derived from occipital myotomes (1–2 and 2–5, respectively).

Figure 3-2.

Head musculature. The cranialmost somitomeres give rise to voluntary musculature of the eye, face, and pharynx. ...

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