Axial Skeleton and Bone Classification

Skeleton Components

• The skeleton is divided into two main parts:

  • Axial Skeleton: Forms the central axis of the body; includes the Skull (cranial and facial portions), Thoracic Cage (sternum and ribs), and Vertebral Column.

  • Appendicular Skeleton: Composed of the appendages; includes the Pectoral Girdle (clavicle, scapula), Upper Limbs (humerus, ulna, radius, carpals, metacarpals, phalanges), Pelvic Girdle (hip bones), and Lower Limbs (femur, patella, tibia, fibula, tarsals, metatarsals, phalanges).

Classification of Bones by Shape

• Long Bones: Longer than they are wide, with a shaft and two ends (e.g., humerus, femur).

• Short Bones: Cube-shaped (e.g., bones of the wrist and ankle).

  • Sesamoid Bones: A type of short bone that forms within tendons (e.g., patella).

• Flat Bones: Thin, flattened, and slightly curved (e.g., sternum, most skull bones).

• Irregular Bones: Have complicated shapes that do not fit other categories (e.g., vertebrae, hip bones).

• Sutural (Wormian) Bones: Small, irregular bones found within sutures of the skull.

Cranial Bones and Sutures

• There are $8$ cranial bones forming the cranium:

  • Single bones: Occipital, Frontal, Sphenoid, Ethmoid.

  • Paired bones: Parietal ($2$), Temporal ($2$).

• Cranial bones are connected by immovable joints called sutures.

  • Major sutures include: Coronal, Sagittal, Lambdoid, and Squamous sutures.