Connective Tissue is the tissue that supports and connects the various parts of the body. Originating primarily in the cells of the mesodermal (middle tissue) layer of the embryo (see Embryology), it forms such varied types of tissue as bone, cartilage, fat, ligaments, and tendons. Connective tissues are composed of a variable structure of cells and fibers surrounded by an intercellular matrix that may be a fluid, solid, or gel, depending on the function of the particular connective tissue. White fibrous connective tissue forms most of the tendons and ligaments. Yellow elastic connective tissue forms such structures as the pads between the vertebrae and the elastic elements of the arterial walls and the trachea. Among other types of connective tissue, cartilage takes part in the formation of joints and the development of bone, and fat tissue provides a cushion for the support of such vital organs as the kidneys and stores excess food for use when needed. Lymphatic tissue (see Lymph) and blood are clearly related in embryonic development to the connective tissues.