The superficial fascia is a fibrous, fatty covering that underlies the skin and is attached to it by fibrous strands. In the scalp, the back of the neck, the palms of the hands, and the soles of the feet, its attachment to the skin is very firm. In all other parts it is loose enough to allow the skin to move freely around; and its elasticity enables it to bring the skin back into place again. The thickness of the superficial fascia depends upon the quantity of fat in its meshes, and therefore varies greatly in the bodies of different individuals and in different parts of the same body; fat is absent from the parts of it that underlie the skin of the eyelid, the nipple and areola of the breast, and some parts of the external genital organs.
The deeper parts of the glands of the skin and of the roots of the hairs penetrate into the superficial fascia, and the mammary glands, which are composed of modified and enlarged skin glands, is developed in it.
In some regions – for example, in the groin – the deeper part of the superficial fascia is in the form of a distinct membranous layer. In two regions, it contains a thin sheet of muscle: (1) in the front and side of the neck and the adjacent part of the chest, where the sheet of muscle is called the platysma; and (2) in the scrotum, where it is called the dartos.
The superficial fascia is a warm garment underneath the skin, for fat is a bad conductor of heat. When moderately fatty, it fills up the hollows and rounds off the irregularities at the surface of the body. In a muscular man, however, it is seldom thick enough to obscure the outlines of the muscles that lie near the surface, whereas it is usually thick enough to do so in women. The rounded contours and smooth outlines of a woman's figure, due to the greater quantity of fat in the superficial fascia, are a secondary sex-character.
The superficial fascia contains also the cutaneous blood vessels, lymph vessels, and nerves on their way to and from the skin; and a few lymph glands are embedded in it.