Fascia is a sheet of connective tissue occurring beneath the skin and also enveloping glands, vessels, nerves, and forming muscle and tendon sheaths. The fascia of the body may be divided into two types: superficial and deep.
The superficial fascia, or subcutaneous tissue, is a mixture of loose areolar tissue and denser, fatty adipose tissue that unites the dermis of the skin to the underlying deep fascia. In the scalp, the back of the neck, the palms of the hands, and the soles of the feet, it contains numerous bundles of collagen fibers that hold the skin firmly to the deeper structures. In the eyelids, auricle of the ear, penis, scrotum, and clitoris, it is devoid of adipose tissue. The thickness of the superficial fascia depends upon the quantity of fat in its meshes, and therefore varies greatly in different bodies and in different parts of the same body.
The deep fascia is a membranous layer of connective tissue that invests the muscles and other deep structures. In the neck it forms well-defined layers, which may play an important part in determining the path taken by pathogenic organisms during the spread of infection. In the thorax and abdomen it is merely a thin film of areolar tissue covering the muscles and aponeuroses. In the limbs it forms a definite sheath around the muscles and other structures, holding them in place. Fibrous septa extend from the deep surface of the membrane, between the groups of muscles, and in many places divide up the interior of the limbs into compartments. In the region of joints the deep fascia may be considerably thickened to form restraining bands called retinacula. Their function is to hold underlying tendons in position or to serve as pulleys around which the tendons may move.
Fascilitis is inflammation of the fascia. It may result from bacterial infection or from a rheumatic disease, such as Reiter's syndrome or ankylosing spondylitis.