The adult human skeleton consists of 206 bones divided into the axial skeleton (skull, vertebral column, thoracic cage) and appendicular skeleton (limbs and girdles). Bone is a dynamic connective tissue composed of an organic matrix (primarily collagen) and inorganic mineral (hydroxyapatite), giving it both flexibility and compressive strength. Bones are classified by shape (long, short, flat, irregular, sesamoid) and are organized internally into compact cortical bone and spongy trabecular bone. Joints (fibrous, cartilaginous, synovial) connect bones and determine range of motion.
Use a labeled skeleton model or 3D anatomy app to identify all major bones and bony landmarks. Grouping bones by region and memorizing landmark terminology together (e.g., the epicondyles and processes of the humerus) is more efficient than rote listing.
From your study of tissue types and histology, you know that bone is a specialized connective tissue — meaning it has cells suspended in an extracellular matrix. What makes bone distinctive is the composition of that matrix: roughly one-third organic material (mainly type I collagen fibers) and two-thirds inorganic mineral (primarily hydroxyapatite, a calcium-phosphate crystal). The collagen gives bone its flexibility and resistance to tension; the mineral gives it hardness and compressive strength. This composite design means bone resists forces from many directions without being brittle like pure mineral or floppy like pure collagen. A green-stick fracture in a child's bone — which bends rather than snapping cleanly — illustrates the collagen component dominating when the mineral content is lower.
The skeleton is conventionally divided into two functional units. The axial skeleton (80 bones) forms the central axis: skull, vertebral column (26 bones including 7 cervical, 12 thoracic, 5 lumbar, sacrum, and coccyx), and thoracic cage (12 pairs of ribs plus the sternum). It protects the brain, spinal cord, and thoracic organs. The appendicular skeleton (126 bones) consists of the limbs and the two girdles that attach them to the axial skeleton — the pectoral girdle (clavicle and scapula) and pelvic girdle (fused hip bones). This division matters clinically because the two units face very different mechanical loads: the axial skeleton bears compressive weight (hence the vertebral discs as shock absorbers), while the appendicular skeleton is engineered for leverage and mobility.
Bone shape follows function. Long bones (humerus, femur, tibia) have a diaphysis (shaft) of dense cortical bone encasing a medullary cavity — this hollow tube design maximizes strength for its weight, just as an engineering I-beam beats a solid rod. The flared ends (epiphyses) are capped with articular cartilage and packed with trabecular (spongy) bone — a lattice of bony struts oriented along lines of mechanical stress, absorbing and distributing load. Flat bones (skull, scapula, sternum) sandwich a layer of spongy bone (diploë) between two cortical plates — efficient for protection and attachment. Short bones (carpals, tarsals) are mostly spongy bone and allow multidirectional mobility in compact spaces.
Joints are where bones interact, and the joint type determines the range of motion. Fibrous joints (skull sutures) allow almost no movement. Cartilaginous joints (intervertebral discs, pubic symphysis) allow limited compression and bending. Synovial joints — the kind you think of when you flex a knee or rotate a shoulder — are the most complex and mobile: the articulating surfaces are covered in smooth hyaline cartilage, enclosed in a joint capsule lined with synovial membrane, and bathed in synovial fluid that acts as both lubricant and nutritional supply for the avascular cartilage. The geometry of the bony surfaces determines the joint's freedom: a ball-and-socket (shoulder, hip) moves in all planes; a hinge (elbow, knee) is constrained to one axis; a pivot (atlas-axis joint) allows rotation only. These mechanical constraints emerge directly from the bony anatomy — learning the shape of a joint surface tells you its degree of freedom.