connective tissue, supportive tissue widely distributed in the body, characterized by large amounts of intercellular substance and relatively few cells. The intercellular material, or matrix, is produced by the cells and gives the tissue its particular character. Connective tissue is diversified in function and may be divided into four categories according to the type of matrix. In connective tissue proper (which forms the framework for most organs) the matrix is soft. In cartilage it is firm but flexible. The intercellular substance of bone, which is high in mineral salts, is rigid. Blood and lymph have a fluid matrix. Three kinds of fibers generally form the supportive material in connective tissue proper. White, or collagenous, fibers vary in size and are composed of fine, parallel fibrils; reticular fibers are small, branching fibers that take on a meshlike pattern; yellow, or elastic, fibers are highly flexible and are capable of branching and anastomosing (or opening) directly into one another. Loose, or areolar, connective tissue is composed of all three of the above fibers; it supports most of the organs in the body and is widely distributed under the skin. The type of connective tissue that forms tendons, ligaments, and fascia is composed mainly of collagenous fibers. It is known as compact tissue. Reticular connective tissue forms the bone marrow and the framework for lymphoid tissue. Adipose, or fat, tissue serves as a cushion for various organs and as a fat reservoir. The colored area of the eye, or iris, is composed of pigmented connective tissue.