Appendicular Skeleton: Structure and Function

Appendicular Skeleton

Overview

The appendicular skeleton consists of the bones of the limbs and the girdles that attach them to the axial skeleton. It is essential for movement and manipulation of the environment. The appendicular skeleton has four major parts:

• Pectoral (Shoulder) Girdles

• Upper Limbs

• Pelvic (Hip) Girdle

• Lower Limbs

Key Point: The appendicular skeleton enables a wide range of motion and supports the weight of the body during movement.

Pectoral (Shoulder) Girdle

Structure and Function

The pectoral girdle attaches the upper limbs to the trunk and provides attachment points for muscles that move the upper limbs.

• Clavicle (Collarbone): S-shaped bone that acts as a strut to hold the scapula in place.

• Scapula (Shoulder Blade): Flat, triangular bone that provides attachment for arm and chest muscles.

Example: The clavicle articulates medially with the sternum and laterally with the scapula.

Upper Limb

Brachium (Upper Arm)

The upper arm contains a single long bone:

• Humerus: The largest bone of the upper limb, articulating proximally with the scapula and distally with the radius and ulna.

Key Point: The humerus forms the ball-and-socket joint at the shoulder and the hinge joint at the elbow.

Antebrachium (Forearm)

The forearm consists of two parallel bones:

• Radius: Located on the lateral (thumb) side of the forearm.

• Ulna: Located on the medial (pinky) side of the forearm.

Key Point: The radius and ulna are connected by an interosseous membrane and articulate with each other at the proximal and distal radioulnar joints.

Hand

The hand is composed of three groups of bones:

• Carpals (Wrist Bones): Eight small bones arranged in two rows.

• Metacarpals (Palm Bones): Five bones numbered I–V from thumb to little finger.

• Phalanges (Finger Bones): Fourteen bones in total; each finger has three phalanges (proximal, middle, distal) except the thumb, which has two (proximal and distal).

Example: The carpal bones allow for the flexibility and movement of the wrist.

Pelvic (Hip) Girdle

Structure and Function

The pelvic girdle attaches the lower limbs to the axial skeleton and supports the weight of the upper body.

• Hip Bone (Coxal Bone): Each hip bone is formed by the fusion of three bones:

  • Ilium

  • Ischium

  • Pubis

Key Point: The pelvic girdle provides strong support for the attachment of the lower limbs and protects pelvic organs.

Male vs. Female Hip

The male and female pelvis differ in structure and function, reflecting adaptations for childbirth in females.

Characteristics	Female	Male
General Structure and Functional Modifications	Broader, lighter, and shallower; adapted for childbirth	Narrower, heavier, and deeper; adapted for support of heavier build
Bone Thickness	Less thick, smoother	Thicker, more prominent markings
Acetabula	Smaller, farther apart	Larger, closer together
Pubic Arch	Wider angle (80–90°)	Narrower angle (50–60°)

Example: The wider pubic arch in females facilitates childbirth.

Additional info: The appendicular skeleton also includes the bones of the lower limbs (femur, tibia, fibula, tarsals, metatarsals, and phalanges), which are not detailed in these notes but are essential for weight-bearing and locomotion.