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PECTORALIS MUSCLES

Some muscles of the chest allow humans to move their ribs when they breathe others allow the arm to hold a child, throw a baseball, or bench press weights. The muscles which allow humans to perform such movements are not unique to humans, they are typical of tetrapods.

In fish, few muscles are located entirely within fins. Chest and trunk muscles are responsible for most of the movement of fins. (Webster, 1974). The trunk muscles of salamanders still resemble those of fish. There are myoseptae between repeating myotomes and these muscles produce lateral movements of the vertebral column similar to those fish use to swim (Webster, 1974, p. 130). All tetrapods possess latissimus dorsi and pectoralis complexes. Both increase in size from amphibians through reptiles and mammals (Webster, 1974, p. 139). The reptilian pectoralis muscle splits to form the pectoralis major, pectoralis minor, pectoantebrachialis, and xiphohumeralis in mammals (Kardong, p. 387 ). The subclavius muscle is derived from the pectoralis minor in mammals (Weichert, 1970, p. 520).

The pectoralis muscle(s) adduct, flex, and medially rotate the arm. The following drawings depict the pectoralis major and minor.

DRAWING DRAWING

FROG

frog

SALAMANDER

SALAMANDERSALAMANDER

ALLIGATOR

PECTORALIS MUSCLES

CHICKEN

PECTORALIS MUSCLES

PIGEON

OPPOSSUM

PECTORALIS MUSCLES

CAT

PECTORALIS MUSCLES

PECTORALIS MUSCLES

GOAT

PECTORALIS MUSCLES

PECTORALIS MUSCLES

SHEEP

PECTORALIS MUSCLES

COW

PECTORALIS MUSCLES

PIG

PECTORALIS

In apes (including humans), the pectoralis minor inserts onto the coracoid process instead of the arm (Hartman, 1933)
 

HUMAN MODEL

PECTORALIS MUSCLES

PECTORALIS MUSCLES
PECTORALIS MUSCLES PECTORALIS MUSCLES
PECTORALIS MUSCLES