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.

DRAWING

     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

CUCULLARIS

SALAMANDER

CUCULLARIS

CHICKEN

TRAPEZIUS

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

TRAPEZIUS

TRAPEZIUS

CAT

TRAPEZIUS

TRAPEZIUS

GOAT

TRAPEZIUS

SHEEP

TRAPEZIUS

TRAPEZIUS

COW

TRAPEZIUS

TRAPEZIUS

PIG

TRAPEZIUS

TRAPEZIUS

RHESUS MONKEY

TRAPEZIUS

 

HUMAN MODEL

TRAPEZIUS

 

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

NECK MUSCLES

OPOSSUM

NECK MUSCLES

NECK MUSCLES

CAT

NECK MUSCLES

NECK MUSCLES

GOAT

NECK MUSCLES

SHEEP

NECK MUSCLES

PIG

PIG

STERNOCLEIDOMASTOID

     The primitive levatores arcuum muscle is retained in mammals as the sternomastoid and cleidomastoid (Kardong, p. 386).

CAT

STERNOCLEIDOMASTOID

MONKEY

STERNOCLEIDOMASTOID

HUMAN MODEL

STERNOCLEIDOMASTOID

STERNOCLEIDOMASTOID