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COMPARATIVE ANATOMY HOME	COMPARATIVE ANATOMY TABLE OF CONTENTS		OBL HOME	OBL REFERENCES
	NECK MUSCLES
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).

SHARK		SALAMANDER

CHICKEN

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.
OPOSSUM

CAT

GOAT
SHEEP
SHEEP
COW
PIG
RHESUS MONKEY

HUMAN MODEL
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.
ALLIGATOR

OPOSSUM

CAT

GOAT		SHEEP
PIG
STERNOCLEIDOMASTOID The primitive levatores arcuum muscle is retained in mammals as the sternomastoid and cleidomastoid (Kardong, p. 386).
CAT		MONKEY

HUMAN MODEL