Connective tissue, also called areolar, fibrous and elastic tissue, is the most widely diffused of all the tissues of the body ; besides enveloping all the muscles, it forms a sheath for each. It also forms partitions between muscles, thus separating as well as connecting them ; it also encloses vessels and nerves, and covers bones and cartilage. It is a membrane formed of cells, with a great deal of substance between them. It is the difference in this intercellular substance which gives the varieties of tissue.

Areolar tissue invests the muscles, nerves, bloodvessels, and other parts, and is continuous throughout the body ; it forms a layer immediately under the skin, and also under the membrane that lines the internal cavities. It consists of two forms of fibres mixed in varying proportions, white and yellow ; these fibres cross each other in every direction, having open spaces between them, hence the name ; the cells lie in the spaces. In some parts areolar tissue is of loose texture, and in others it is close, thus providing for the requirements of the parts it encloses.

White fibrous tissue is found almost entirely in ligaments and tendons and the covering of bones and cartilage. In the form of a membrane it binds down muscles, and takes the name of fascia and aponeurosis; its structure is much the same as that of areolar tissue, but the fibres adhere more closely, and generally run in one direction instead of interlacing. It is white and shining, strong, tough, and inextensile.

Yellow elastic tissue is not so strong, but it is elastic ; it is found in the walls of bloodvessels and air-tubes, and unites the cartilages of the larynx. The ligamentum subflava, which forms bands between some of the vertebrae, is composed of

this tissue. It differs in structure from the others in having a preponderance of elastic fibres.

The subcutaneous connective tissue is called superficial fascia ; as well as having fat deposits, it is ramified by cutaneous vessels and nerves before they enter the skin. Beneath this there is another layer of fibrous tissue, which closely invests the muscles, called deep fascia.

Adipose tissue comes under the head of connective tissue, because it is in the subcutaneous connective tissue the fat cells are scattered. Fat collects in some parts of the body more than in others ; it fills up spaces and gives roundness to the figure ; as it is a bad conductor of heat, it serves to keep the body warm.