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Division of the Human Skeleton: Axial & Appendicular

• Axial Skeleton: 80 bones
• Appendicular Skeleton: 126 bones

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PART 1 - AXIAL SKELETON (80 Bones)

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A. SKULL (22 Bones)

1. Cranial Bones - Neurocranium (8 bones)

2. Facial Bones - Viscerocranium (14 bones)

Note: The mandible is NOT part of the cranium or formal facial skeleton in some classifications but is counted among the 22 skull bones.

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B. EAR OSSICLES (6 Bones)

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C. HYOID BONE (1 Bone)

• U-shaped bone at the base of the tongue
• The only bone in the body that does not articulate with any other bone
• Supports the tongue and serves as attachment for muscles of the floor of the mouth

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D. VERTEBRAL COLUMN (26 Bones)

• Vertebral body - anterior; major weight-bearing component; increases in size from C2 to L5
• Vertebral arch - formed by two pedicles (lateral pillars) and two laminae
• Spinous process - projects posteriorly from arch (posterior midline)
• Transverse processes - extend laterally
• Articular processes - superior and inferior; articulate with adjacent vertebrae
• Vertebral foramen - forms the vertebral canal when stacked

• C1 (Atlas) - ring-shaped, no body, supports skull
• C2 (Axis) - has dens (odontoid process) that projects into C1
• C7 (Vertebra prominens) - longest spinous process, easily palpable

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E. THORACIC CAGE (25 Bones)

Ribs (24 = 12 pairs)

• Head - articulates with vertebral body
• Neck - narrow part adjacent to head
• Tubercle - articulates with transverse process of vertebra
• Shaft (body) - main curved portion; has costal groove on inferior inner border (neurovascular bundle runs here)

Sternum (1 bone)

• Sternal angle (Angle of Louis) - junction of manubrium and body; at level of T4/T5 disc; rib 2 attaches here

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PART 2 - APPENDICULAR SKELETON (126 Bones)

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A. PECTORAL (SHOULDER) GIRDLE (4 Bones)

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B. UPPER LIMB (60 Bones = 30 per side)

Arm (1 bone/side)

Forearm (2 bones/side)

Wrist - Carpal Bones (8/side = 16 total)

Note: Scaphoid is the most commonly fractured carpal bone (fall on outstretched hand)

Hand

• Thumb: proximal + distal (2 phalanges)
• Fingers 2-5: proximal + middle + distal (3 phalanges each)

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C. PELVIC (HIP) GIRDLE (2 Bones)

• Ilium - large flared upper part; iliac crest is palpable
• Ischium - inferior-posterior; forms ischial tuberosity ("sitting bone")
• Pubis - anterior; two pubic bones meet at pubic symphysis
• Acetabulum - cup-shaped socket at junction of all 3 bones; receives femoral head

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D. LOWER LIMB (60 Bones = 30 per side)

Thigh (1 bone/side)

Kneecap (1 bone/side)

Leg (2 bones/side)

Ankle - Tarsal Bones (7/side = 14 total)

Foot

• Big toe (hallux): proximal + distal (2 phalanges)
• Toes 2-5: proximal + middle + distal (3 each)

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SUMMARY TABLE: 206 Bones at a Glance

Axial Skeleton (80 Bones)

Appendicular Skeleton (126 Bones)

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Key Clinical Points

• Intramembranous - direct bone deposition without cartilage model (e.g., skull flat bones, clavicle)
• Endochondral - bone replaces a cartilage precursor (most bones); begins at primary ossification centers in diaphyses, mostly present at birth; secondary ossification centers develop at epiphyses and are sites of physeal (growth plate) fractures in children

• Red marrow (active hematopoiesis) - first develops in appendicular skeleton, later in axial skeleton in adults
• Yellow marrow (inactive; ~80% fat) - replaces red marrow peripherally with age

• Long bones - femur, humerus, metacarpals, phalanges
• Short bones - carpals, tarsals
• Flat bones - skull, scapula, sternum, ribs
• Irregular bones - vertebrae, hyoid, facial bones
• Sesamoid bones - patella (largest), pisiform

• The femur is the longest and strongest bone
• The hyoid is the only bone that articulates with no other bone
• The stapes is the smallest bone in the body
• The patella is the largest sesamoid bone
• The scaphoid is the most commonly fractured carpal bone

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• Cover summary badges showing total count at a glance: 206 total, 80 axial, 126 appendicular
• Part 1 - Axial Skeleton (80 bones) organized into 6 sections:
  • Cranial bones (8) - Facial bones (14) - Ear ossicles (6) - Hyoid (1) - Vertebral column (26) - Thoracic cage (25)
• Part 2 - Appendicular Skeleton (126 bones) organized into 8 sections:
  • Pectoral girdle (4) - Upper limb arm/forearm (6) - Carpals/wrist (16) - Metacarpals + hand phalanges (54) - Pelvic girdle (6) - Lower limb thigh/knee/leg (8) - Tarsals/ankle (14) - Metatarsals + foot phalanges (56)
• Every bone listed with its exact position in the body and quantity
• Final tally table summarizing all counts that add up to 206
• Color-coded tables, alternating row shading, and running page headers throughout

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• Bone name + Latin term
• Position in the skull
• Full key features and landmarks

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Lateral View (Left) — 6 bones visible:

Anterior View (Right) — deeper bones revealed:

Sutures Labeled:

• Coronal — Frontal/Parietal junction
• Sagittal — Between the two Parietal bones (midline)
• Squamous — Parietal/Temporal junction
• Lambdoid — Parietal/Occipital junction

Note: The Ethmoid bone is deep and only seen in the anterior/internal views. The Parietal and Temporal bones each appear as a pair (×2), making the total count = 8 bones.