Kierszenbaum, A.( 2002). Histology and Cell Biology. Connective Tissues. Philadelphia, USA:Mosby Inc. page95Connective tissues are classified into three major groups which are: embryonicconnective tissue, adult connective, and special connective tissue. Embryonicconnective tissue is a loose tissue formed during early embryonic development that wasfound primarily in the umbilical cord. Adult connective tissue has considerable structuraldiversity because of proportion of cells to fibers and of and of ground substance variesfrom tissue to tissue. There are two sub classifications of this type of connective tissue.Those are loose connective tissue that contains more cells than collagen fibers anddense connective tissue that contains more collagen fibers than cells. There are threemain types of loose connective tissue: Collagenous fibers are made of collagen andconsist of bundles of fibrils that are coils of collagen molecules, Elastic fibers are madeof elastin and are stretchable, and Reticular fibers join connective tissues to other tissues. On the other hand, special connective tissue, comprises types of connectivetissue with specialized properties not observed in the embryonic connective tissue or inthe adult connective tissue proper. There are four types of specialized connective tissueans those are: Adipose, Cartilage, Bone , and Blood. Adipose tissue is a form of looseconnective tissue that stores fat. Cartilage is a form of fibrous connective tissue that iscomposed of closely packed collagenous fibers in a rubbery gelatinous substancecalled chondrin. Bone is a type of mineralized connective tissue that contains collagenand calcium phosphate, a mineral crystal. Interestingly enough, blood is considered tobe a type of connective tissue.