Connective tissue blood vessels. Coloured scanning electron micrograph (SEM) of a resin cast of blood vessels in a type of connective tissue called the perichondrium. This tissue surrounds the cartilage of developing bones. The blood vessels bring oxygen and building materials to the tissue, aiding the growth of the new bone, and remove waste products. The cast was made by injecting resin into the blood vessels. The surrounding tissues were then chemically digested.