By Kevin Beck | Updated Mar 24, 2022

In a fully mature human adult the skeleton is comprised of 206 distinct bones. This number is a result of many developmental processes, including the fusion of certain skull bones after birth. Anatomy scholars categorize these bones into two main divisions: the axial skeleton (head, neck, chest, back) and the appendicular skeleton (arms, legs, pelvis, shoulder girdle). 172 of the 206 bones are paired, while 34 remain unpaired.

Axial Skeleton

The axial skeleton contains 80 bones. It includes the skull (28 bones), the vertebral column (26 bones), the rib cage (24 ribs plus the sternum), and the hyoid bone. The skull’s 28 bones comprise 22 paired bones (e.g., the frontal and parietal bones) and six midline bones (e.g., the mandible and the sphenoid). The vertebral column protects the spinal cord and is made up of 7 cervical, 12 thoracic, and 5 lumbar vertebrae, plus the sacrum and coccyx. Twelve pairs of ribs encircle the thoracic cage, and the sternum anchors the ribs anteriorly.

Appendicular Skeleton

The appendicular skeleton contains 126 bones, providing attachment points for muscles and facilitating movement. Hands and feet alone account for 106 of these bones. Each hand has 27 bones: 8 carpals, 5 metacarpals, and 14 phalanges. Each foot has 26 bones: 7 tarsals, 5 metatarsals, and 14 phalanges. Upper‑body appendages include the shoulder girdle (scapula and clavicle) and the arm (humerus, radius, ulna). Lower‑body appendages contain the pelvis (ilium, ischium, pubis), femur, patella, tibia, and fibula.

Key Functions of Bones

• Structural support and shape
• Protection of vital organs (brain, heart, lungs, spinal cord)
• Attachment points for muscles, enabling locomotion
• Production of blood cells within marrow (hematopoiesis)
• Storage of minerals such as calcium and phosphorus
• Release of fat and minerals into the bloodstream when needed

Remembering Bone Names: Mnemonics

Mnemonic devices help students recall complex lists. For example:

• Unpaired skull bones: Frontal, Parietal, Occipital, Temporal, Sphenoid, Ethmoid – phrase: "Fraternity Parties Occasionally Teach Spam Etiquette".
• Eight wrist bones: scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate – phrase: "Stop Letting Those People Touch The Cadaver's Hand".
• Seven ankle bones: talus, calcaneus, navicular, medial cuneiform, intermediate cuneiform, lateral cuneiform, cuboid – phrase: "Tall Californian Navy Medical Interns Like Candy".

Early Development of the Skeleton

Several skull bones remain unfused during infancy, forming soft spots known as fontanelles. These gaps allow the skull to flex during birth and accommodate rapid brain growth. Typically, the sutures fuse by age two, resulting in the adult count of 206 bones. Rarely, premature fusion—craniosynostosis—occurs in about 1 in 2,000 births, usually in males. Early surgical intervention corrects the condition and permits normal cranial development.