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REFERENCES |
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BACK
AND NECK MUSCLES
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Humans possess a number of muscles which
allow them to move their backs when they dance, play sports, and get out
of bed in the morning. Humans possess
a number of muscles which allow them to move their neck whether they are
turning to look at a friend, bowing their heads in prayer, or looking
up at the stars. The muscles which allow humans to perform such
movements are not unique to humans, they are typical of vertebrates.
The ancestors of vertebrates had axial musculature
which is divided into segments (myomeres) as in the early Cambrian chordate
and jawless fish depicted below
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The axial musculature of Amphioxus and the lampreys retain this organization
of myomeres, as is evident in the following image
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LAMPREY
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| In
cartilaginous fish, the myotomes are separated into dorsal epaxial and ventral
hypaxial divisions. (Weichert, 1970). These
layers are illustrated in the shark below. |
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epaxial muscles act to extend and laterally flex the back. In fish and salamanders, this epaxial musculature
is important for the lateral flexing of the back they depend on for locomotion.
The development of limbs decreased the importance of the epaxial
muscles. |
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In
amphibians, the epaxial musculature is represented by a single muscle, the
dorsalis trunci. In amniotes, this sheet of muscle is called the erector
spinae and is divided into medial, intermediate, and lateral groups. This dorsalis trunci also contains components
of logissimus dorsi, intertransversarial, and interneural muscles found
in amniotes. (Weichert, 1970, p. 511). Amphibians and amniotes also possess interspinalis
muscles derived from epaxial musculature (Webster, 1974).
FROG
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SALAMANDER
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SALAMANDER
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| In reptiles, the erector spinae is composed
of iliocostalis (lateral), longissimus (middle) and transversospinalis (medial)
groups. In the neck region, the longissimus
forms the cervicus capitus muscle. Reptiles
also possess transversospinalis muscles from which occipital muscles are
derived. (Webster,
1974). |
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ALLIGATOR
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. In mammals, the lateral undulation of the vertebral
column is greatly reduced in locomotion and the epaxial muscles of the
erector spinae become even less important.
Mammalian muscles are similar to those found in reptiles but the
anterior muscles are split into a greater number of subdivisions. (Webster,
1974). The multifidus is
a mammalian remnant of transversospinalis muscles in reptiles (Weichert,
1970, p. 513).
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OPOSSUM
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CAT
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GOAT
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SHEEP
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COW
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RHESUS MONKEY
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