The Appendicular Skeleton: Upper Limb and Shoulder Girdle

Shoulder Girdle (Pectoral Girdle)

The shoulder girdle, responsible for connecting the upper limbs to the axial skeleton, comprises two bones on each side of the body. These are the clavicle (collarbone) and the scapula (shoulder blade). Each clavicle is a long bone with an S-shape, articulating medially with the sternum and laterally with the acromion process of the scapula. The scapula, a flat triangular bone, provides attachments for numerous muscles and ligaments involved in arm movement.

Upper Limb Bones

Each upper limb contains 30 bones, categorized as follows:

Arm

• Humerus: A long bone forming the upper arm, articulating proximally with the scapula at the glenohumeral joint and distally with the radius and ulna at the elbow joint.

Forearm

• Radius: The lateral bone of the forearm, articulating with the humerus and the carpal bones of the wrist. Its position is crucial for pronation and supination.
• Ulna: The medial bone of the forearm, articulating with the humerus and the carpal bones. It plays a significant role in elbow stability.

Hand

• Carpals (Wrist): Eight small, short bones arranged in two rows, facilitating wrist flexibility and movement.
• Metacarpals (Palm): Five long bones forming the palm of the hand, each articulating with a carpal bone proximally and a phalanx distally.
• Phalanges (Fingers): Fourteen bones composing the fingers. Each finger (except the thumb) has three phalanges: proximal, middle, and distal. The thumb has only two phalanges: proximal and distal.

Bone Articulations and Movements

The bones of the upper limb and shoulder girdle are interconnected via a complex network of joints, allowing for a wide range of movements including flexion, extension, abduction, adduction, rotation, and circumduction. The precise mechanics of these movements are facilitated by the shapes and orientations of the bones, along with the action of numerous muscles and ligaments.