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Objectives
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.
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There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle.
Nearly all muscle is derived from mesoderm.
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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).
Each somite gives rise to three parts: dermatome, myotome, and sclerotome.
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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.
The intrinsic laryngeal muscles and tongue musculature are derived from occipital myotomes (1–2 and 2–5, respectively).
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