Copyright Goodheart-Willcox Co., Inc. Chapter 5 The Skeletal System 123 Shapes of Bones Because of the large variety of sizes and shapes of the bones in the human skeleton, bones are tradi- tionally divided into five categories for the purpose of discussion (Figure 5.3): • Long bones have a long, somewhat cylindrical shaft made of cortical bone, with bulbous knobs of trabecular bone encased in cortical bone at both ends. The shaft encloses the central hollow medullary cavity or canal. The major bones of the arms and legs are long bones. Properties of Bone Tissue Cortical Bone Trabecular Bone Structure dense porous (honeycomb structure) Mineral content relatively high relatively low Strength relatively high low Flexibility low relatively more Shock-absorbing ability low relatively more Primary locations outer surface of all bones, long bones of limbs interior of vertebrae, femoral neck, wrist, and ankle bones Figure 5.2 Goodheart-Willcox Publisher Short bones Long bone Irregular bone Sesamoid bone Flat bone © Body Scientific International Figure 5.3 The five shape categories of bones.