- Appendicular skeleton is composed of bones which lie on the lateral sides of the mid axial line (Axial skeleton) of our body and consists of the hanging bones.
- It can be divided into two groups;
- The upper extremities (Pectoral girdle and the bones of upper limbs)
- The lower extremities (Pelvic girdle and the bones of lower limbs)
*Girdle is the bony or cartilaginous arch that supports the limbs of the vertebrates.
The upper extremities (64 bones):
- The upper extremity is connected to and supported by the axial skeleton by only one joint (pectoral girdle or the shoulder joint) and many muscles.
- The joint is the sternoclavicular joint between the manubrium of the sternum and the clavicle.
- The upper extremities consist of 64 bones which include;
- Clavicle (2 bones):
- It is a collar bone, double curved long bone with rounded medial end and flattened lateral end.
- It holds the shoulder joint and arm away from thorax so upper limb can swing freely.
2. Scapula (2 bones):
- It is a shoulder blade which is flat and triangular with horizontal spine separating fossae.
- It is the site of attachment of muscles of arm and chest.
- The glenoid fossa receives the head of humerus.
- Humerus (2 bones):
- It is the longest and the largest bone of the upper limb.
- It forms ball and socket joint with the glenoid fossa of scapula.
- Muscles of the shoulder and arm attach to the humerus permitting arm to flex and extend at elbow.
- Radius and ulna (4 bones):
- There are 1 radius and 1 ulna in each forearm respectively.
- Radius is the shorter of two bones present in forearm.
- It allows forearm to rotate in radial motion.
- Ulna is the larger of the two bones in forearm.
- Larger proximal end consists of olecranon process (prominence of elbow).
- It forms hinge joint at the elbow.
- Carpals (16 bones):
- There are 8 carpals in each wrist.
- They are small and short bones.
- 8 carpals are arranged in 2 transverse rows of 4.
- They help in slight gliding movement because of attached ligaments.
- Metacarpals (10 bones):
- They are five miniature long bones in each hand in fan like arrangement.
- They articulate with the fingers at metacarpo-phallangeal joint (the knuckles).
- They aid in opposition movement of thumb and enable cupping of hand.
- Phalanges (28 bones):
- There are 14 phalanges in each hand.
- They are miniature long bones; 2 in each thumb and 3 in each finger.
- They articulate with each other at inter-phalangeal joint and allow fingers to participate in stable grips.
The lower extremities (62 bones):
- It can be divided into two parts; the pelvic girdle or the hip joint and the bones of lower limbs.
- The lower extremities consist of 62 bones which include:
- Pelvic girdle (2 bones):
- The bone is called pelvis or hip bone or coxa.
- It is an irregular bone formed by the fusion of ilium, ishium and pubis (which are separate in children).
- The hip bone is fused with the sacrum and coccyx to form a pelvis.
- The head of femur fits into the acetabulum in the pubis of hip bone to form a ball and socket joint.
- Pelvis girdle is also the site of attachment of trunk and lower limb muscles.
- It also transmits body weight to femur.
- Femur (2 bones):
- It is a typical long bone in the thigh (also called a thigh bone).
- It is the longest, strongest and heaviest bone.
- It forms a ball and socket joint with the pelvic bones.
- Femur provides articular surfaces for knee and supports the body.
- Patella (2 bones):
- This is the bone present in each knee.
- It is roughly triangular or circular flat sesamoid bone (developed from the tendon quadriceps femoris).
- It increases the leverage for quadriceps muscle by keeping tendon away from the axis of rotation.
- It protects the knee joint.
- Tibia and fibula (4 bones):
- There are 1 tibia and 1 fibia in each leg respectively.
- Tibia is the larger long bone of the lower leg (calf region) which articulates with the femur, fibula and tarsals.
- It supports the body weight transmitting it from femur to the tarsals.
- Fibula is the smaller long bone of the lower leg.
- It articulates proximally with tibia and distally with tarsals.
- It bears little body weight but gives strength to the ankle joint.
- Tarsals (14 bones):
- They are short bones in the ankle region (also called the heelbones).
- They are 7 in each ankle and with the metatarsals form the arches of foot.
- They also bear body weight, raise the body and transmit thrust during running and walking.
- Metatarsals (10 bones):
- They are miniature long bones, 5 in each foot and form the sole.
- With tarsals, they form arches of feet and also improve stability while standing.
- Metatarsals also absorb shocks, bear weight and aid in locomotion.
- Phalanges (28 bones):
- There are 14 phalanges in each foot.
- They are the miniature long bones in the toes.
- They are arranged as in hand (2 in each big toe and 3 in each other toe).
- They provide stability during locomotion.
