In the human body, the appendicular skeleton is unfused (unlike the axial skeleton), which allows for a much greater range of motion. The appendicular skeleton is composed of 126 bones. The word "appendicular" comes from "appendage," which means "a part that is joined to something larger." The appendicular skeleton comprises the limbs and their supporting girdles (pectoral and pelvic).
Functionally, the appendicular skeleton is involved in locomotion (lower limbs) and manipulation of objects in the environment (upper limbs).
The appendicular skeleton is divided into six major regions [fig:565]:
- Pectoral Girdle (four bones). The pectoral girdle consists of the left and right clavicle (two bones) and the left and right scapula (two bones).
- Upper arm and Forearm (six bones). This consists of the left and right Humerus (two bones in the upper arm), the ulna (two bones), and the radius (two bones). Both the ulna and the radius are in the forearm.
- Hand and wrist (54 bones). There are many constituents in the hand and wrist; the left and right carpals (16 bones in the wrist), Metacarpals (10 bones), Proximal phalanges (10 bones), Middle phalanges (eight bones), and Distal phalanges (10 bones). The relative placement of the hand bones can be seen in Figure 2.
- Pelvic Girdle (two bones) - The pelvic girdle consists of the left and right os coxa, or the hip bone (two bones). In some vertebrates, including humans, the ox coxa is comprised of three bones: the ilium, ischium, and pubis.
- Thigh and leg (eight bones) - The thigh and leg consist of the femur (two bones that comprise the thighs), Tibia (two bones), Patella (two bones that are the knees), and Fibula (two bones). These bones are diagrammed in Figure 3.
- Feet and ankle (52 bones) - The feet and ankle consist of the tarsals (14 bones in the ankle), Metatarsals (10 bones), Proximal phalanges (10 bones), Middle phalanges (eight bones), and Distal phalanges (10 bones).
Note that these areas may include other bones that are not a part of the appendicular skeleton; they are instead a part of the axial skeleton.