Fibrosis in the lung replaces functioning lung tissue with fibrous connective tissue. Bone tissue is a type of dense connective tissue. It consists of loose connective tissue and elastin. Desmoplasia refers to growth of dense connective tissue or stroma. Fibromas are benign tumors that are composed of fibrous or connective tissue. Tendons are categorized as a connective tissue. Beneath the mucosa lies the submucosa, consisting of fibrous connective tissue. Its small cells form irregular cords and clusters, separated by capillaries and connective tissue. Like other cells of connective tissue, fibroblasts are derived from primitive mesenchyme. These cells are grouped together in lobules separated by connective tissue. They are often due to damage of blood vessels and connective tissue cells. The mesoderm gives rise to many cell types such as muscle, bone, and connective tissue. In contrast, sarcomas develop in connective tissue. The muscular layer is surrounded by a layer of connective and fat tissue. A sarcoma is a cancer that arises from transformed cells of mesenchymal (connective tissue) origin.