The subcutaneous layer is situated below the dermis. It consists of adipose tissue (fat) and areolar tissue. The adipose tissue helps to protect the body against injury and acts as an insulating layer against heat loss, helping to keep the body warm. The areolar tissue contains elastic fibers making this layer elastic and flexible. Muscle is situated below the subcutaneous layer and is attached to bone. The borderline between the deepest layer and the reticular above and is often indistinct. The subcutaneous is made up of adipose tissue (fate cells) loose connective tissue (areolar) because it is so rich in blood vessels, lymphatic vessels and nerve fibers. In both the papillary and the reticular layers of dermis, fibroblasts and fibrocytes (immature fibroblasts) are the cells responsible for lying down and maintaining the extracellular matrix, and hence the structure of the dermis.