124 Introduction to Anatomy & Physiology The long bones in the arms and legs are primarily composed of strong cortical bone tissue, although there is trabecular bone inside the ends. The bones in the spinal column contain a large amount of trabecular bone inside their cortical encasings, giving them a certain amount of shock- absorbing capability. Figure 4.2 compares the properties of these two types of bone tissue. MEMORY TIPP The word cortical (coming from cortex) pertains to the outer layer of something. For example, the outer layer of the brain is known as the cerebral cortex. The outer layer of many structures and objects, including a plant stem or even a rock, is also known as its The type of bone tissue forming the outer layer of bone is therefore called cortical MEMORY e rd cortical g cortex p t e l something. le, t e r layer cerebral cortex e g pl k, al k cocortex.texr g i therefore called cortical bobone.e.n Shape Categories of Bones Because of the large variety of sizes and shapes of the bones in the human skeleton, for purposes of discussion bones are traditionally divided into five categories (Figure 4.3): • Long bones have a long, somewhat round shaft made of cortical bone, with bulbous knobs of trabecular bone encased in cortical bone at both ends. The shafts enclose the central hollow medullary cavity or canal. The major bones of the arms and legs are long bones. • Short bones are shaped like a cube and are composed mainly of trabecular bone. The bones of the wrists and ankles are short bones. Susumu Nishinaga/Science Source, Jose Luis Calvo/Shutterstock.com Figure 4.1 A—A micrograph of trabecular bone tissue. B—Cortical bone tissue. How would you describe the difference between trabecular and cortical bone to someone who knew nothing about these two types of bone tissue? A B Properties of the Two Types 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 4.2 Goodheart-Willcox Publisher Copyright Goodheart-Willcox Co., Inc.