Light micrograph of a longitudinal section through a foetal finger. Foetal bones are initially formed of cartilage (purple). Bone formation (ossification) starts from the middle of the cartilage and proceeds outwards. Areas where bone has already formed are red, areas of active ossification are dark purple. Violet areas at right are bone marrow, a blood forming substance. Across bottom are a tendon and connective tissue. Magnification: x100 when printed at 15cm wide.