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NECK MUSCLES
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TRAPEZIUS In humans, the trapezius extends the
neck and retracts the scapula. |
A pair of trapezius muscles
are present in lancelets on the dorsal surface which helps to expel
water from the body. (Ruppert, from Harrison, 1997, p.
397-9). In amphibians, the
muscles which attached to gills in fish ancestors, such as cucillaris, attach
to the pectoral girdle (Webster, 1974, p.141).
The cucullaris muscle (in the shark and salamander below) is the
homolog of the trapezius muscle in mammals.
The trapezius and cleidomastoid are fused in reptiles (Webster, 1974,
p.138). Thus, the trapezius is the only remnant of a
branchial bar levator which is retained in tetrapods (Romer, p. 307).
Post-otic neural crest (PONC) cells contribute to shoulder and neck structures, as do cells derived from mesoderm. The trapezius and coracobranchial muscles which open and retract the jaw are derived from neural crest cells (Matsuoka, 2005). |
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SHARK |
SALAMANDER |
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CHICKEN |
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In
many mammals, there are three trapezius muscles (clavotrapezius, acromiotrapezius,
and spinotrapezius) which correspond to the three regions of the single
trapezius muscle in humans. |
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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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PIG |
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RHESUS MONKEY |
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HUMAN MODEL |
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NECK There are additional axial muscles in the
dorsal region which extend the neck and (in
quadrupedal animals), raise the head.
Amphibians were the first animals in which the pectoral girdle
was separate from the head (thus, creating a neck).
Necks became longer in amniotes, as did neck muscles. |
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ALLIGATOR |
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OPOSSUM |
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CAT |
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GOAT |
SHEEP |
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PIG |
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STERNOCLEIDOMASTOID The primitive levatores arcuum muscle is
retained in mammals as the sternomastoid and cleidomastoid (Kardong, p.
386). |
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CAT |
MONKEY |
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HUMAN MODEL |
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