Human appendicular skeleton
The appendicular skeleton consists of the bones or cartilage that support the appendages of vertebrates. Appendages appeared as fins in early fishes, and subsequently evolved into the limbs of tetrapods. The appendicular skeleton includes the skeletal elements within the limbs, as well as supporting pectoral and pelvic girdles in the case of tetrapods (these are lacking in fish). The word appendicular is the adjective of the noun appendage, which itself means a part that is joined to something larger.
In humans the appendicular skeleton is composed of 126 bones. Functionally it is involved in locomotion (lower limbs) of the axial skeleton and manipulation of objects in the environment (upper limbs).
The appendicular skeleton forms during development from cartlilage, by the process of endochondral ossification.
The appendicular skeleton is divided into six major regions:
- Pectoral girdles (4 bones) - Left and right clavicle (2) and scapula (2).
- Arms and forearms (6 bones) - Left and right humerus (2) (arm), ulna (2) and radius (2) (forearm).
- Hands (54 bones) - Left and right carpals (16) (wrist), metacarpals (10), proximal phalanges (10), intermediate phalanges (8) and distal phalanges (10).
- Pelvis (2 bones) - Left and right hip bone (2).
- Thighs and legs (8 bones) - Left and right femur (2) (thigh), patella (2) (knee), tibia (2) and fibula (2) (leg).
- Feet and ankles (52 bones) - Left and right tarsals (14) (ankle), metatarsals (10), proximal phalanges (10), intermediate phalanges (8) and distal phalanges (10).
It is important to realize that through anatomical variation it is common for the skeleton to have many extra bones (sutural bones in the skull, cervical ribs, lumbar ribs and even extra lumbar vertebrae).
The appendicular skeleton of 126 bones and the axial skeleton of 80 bones together form the complete skeleton of 206 bones in the human body. Unlike the axial skeleton, the appendicular skeleton is unfused. This allows for a much greater range of motion.
- Skeleton Encyclopaedia Britannica. Updated 24 August 2014.
- Vizniak, N.A., 2008, Quick Reference Clinical Consultant Muscle Manual, Professional Health Systems Inc, Canada
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Anatomy & Physiology By Saladin