Lecture 8: Appendicular System
The appendicular system consists of the upper and lower limbs (appendages), and its primary
function is movement.
Due to their similar developmental programs, the upper and lower limbs have much in
common, as each limb is composed of limb girdles and free limbs.
Upper Limbs: pectoral girdles + free upper limbs
Lower Limbs: pelvic girdles + free lower limbs
The first segments of the free limbs (arm in the upper limb and the thigh in the lower limb),
when compared, both have a single large bone. Proceeding distally to the second segments, the
forearm in the upper limb and the leg in the lower limb both have 2 parallel bones.
At the junctions of these second segments with the hand and the foot (wrist + ankle), there are
numerous small bones (8 in wrist; 7 in ankle), and the hands/feet have the same number and
the arrangement of bones, which form the fingers and toes.
However, the major difference between the upper and lower limbs is that the pelvic girdles of
the lower limb are firmly anchored to the vertebral column via a strong ligamentous joint.
However, the pectoral girdles of the upper limbs don’t form any joints with the vertebral
column – they are instead, only weakly joined to the axial skeleton via junction of the clavicle
(collar bone) with the sternum.
• Skeleton of the Upper Limb:
Each upper limb skeleton consists of 32 bones, which form 2 distinct regions:
1) The pectoral girdle:
- The term, “pectoral”, refers to the chest/breast
- The girdles attach the bones of the free upper limbs to the axial skeleton.
- Each of the 2 pectoral girdles consists of a clavicle and scapula: