Subcutaneous Musculature

a superficial, more or less isolated layer of predominantly trunk parietal and partially visceral striated musculature in terrestrial vertebrates, closely connected with the skin and conditioning its movements.

Subcutaneous musculature is usually poorly developed in amphibians and reptiles, except snakes. In such animals, the large scales, or plates, are equipped with strong bundles of muscle fibers; when these muscle fibers contract, the scales rise, which increases friction between the substratum and the body. In birds, elements of subcutaneous musculature, which have developed from the musculature of the humerus and wing, penetrate the flight membrane of the wing; their contraction aids in flight.

In the majority of mammals, except higher primates, almost the entire trunk and neck are covered with a layer of subcutaneous musculature that has developed from the pectoral muscle, the broad muscle of the back, and the constrictor muscle of the neck. The subcutaneous musculature in mammals permits movement of the skin for driving away insects, turning of the body in armadillos and hedgehogs, movement of the needles in hedgehogs and porcupines, and movement of such tactile hairs as vibrissae. Especially developed is the facial part of subcutaneous musculature of visceral origin, whose fascicles are concentrated around the eye sockets, ears, and lips and form the platysma and mimic musculature in the region of the neck and head. In apes and man, trunk subcutaneous musculature disappears; the mimic musculature has a particularly complex differentiation and is innervated by the facial nerves.