The Appendicular Skeleton: Structure and Function

The Appendicular Skeleton

Overview of the Appendicular Skeleton

The appendicular skeleton consists of the bones that form the upper and lower limbs, as well as the girdles that attach these limbs to the axial skeleton. It plays a crucial role in movement and manipulation of the environment.

• Components: Upper limbs, lower limbs, pectoral (shoulder) girdles, and pelvic girdles.

• Total Bones: 126 bones in the appendicular skeleton.

• Girdle: A structure that encircles or surrounds, providing attachment points for limbs.

Main Divisions of the Appendicular Skeleton

Pectoral (Shoulder) Girdle

The pectoral girdle attaches the upper limbs to the trunk and provides mobility and flexibility to the shoulder region.

• Bones: Clavicle (collarbone) and scapula (shoulder blade).

• Function: Supports the upper limbs and serves as an attachment site for muscles.

• Articulations:

  • Medial end of each clavicle articulates with the manubrium of the sternum.

  • Lateral end of each clavicle joins the scapula.

  • Scapulae do not join each other or the axial skeleton directly.

• Mobility: The pectoral girdle allows a wide range of motion for the upper limbs.

Pelvic Girdle

The pelvic girdle attaches the lower limbs to the trunk and supports the weight of the upper body when sitting or standing.

• Bones: Two hip bones (each formed by the fusion of the ilium, ischium, and pubis), sacrum, and coccyx.

• Function: Supports and protects pelvic organs, provides attachment for lower limbs.

• Structure: The pelvic girdle forms a strong, stable ring that supports the body's weight.

Upper and Lower Limbs

Upper Limb Bones

The upper limb is specialized for mobility and manipulation.

• Regions: Arm (humerus), forearm (radius and ulna), and hand (carpals, metacarpals, phalanges).

• Function: Enables a wide range of movements and dexterity.

Lower Limb Bones

The lower limb is specialized for weight-bearing and locomotion.

• Regions: Thigh (femur), leg (tibia and fibula), and foot (tarsals, metatarsals, phalanges).

• Function: Supports the body's weight and enables walking, running, and jumping.

Comparison of Girdles

Girdle	Bones	Function	Attachment
Pectoral Girdle	Clavicle, Scapula	Attaches upper limbs to trunk; allows mobility	Articulates with sternum (clavicle); scapula floats on back
Pelvic Girdle	2 Hip bones, Sacrum, Coccyx	Attaches lower limbs to trunk; supports weight	Firmly attached to axial skeleton (sacrum)

Functional Differences Between Upper and Lower Limbs

• Upper Limbs: Adapted for flexibility, manipulation, and a wide range of motion.

• Lower Limbs: Adapted for strength, stability, and locomotion.

Pectoral Girdle: Additional Functions

• Protects delicate and vital organs such as the heart and lungs.

• Acts as a surface for the attachment of muscles of the shoulder.

• Maintains the shape of the body and assists in movement, especially during activities like jumping.

Key Terms and Definitions

• Girdle: A bony or cartilaginous structure that encircles the body, providing support and attachment for limbs.

• Pectoral Girdle: The set of bones (clavicle and scapula) that attach the upper limbs to the trunk.

• Pelvic Girdle: The set of bones (hip bones, sacrum, coccyx) that attach the lower limbs to the trunk.

• Axial Skeleton: The central part of the skeleton, including the skull, vertebral column, and rib cage.

• Appendicular Skeleton: The bones of the limbs and girdles that attach them to the axial skeleton.

Summary Table: Bones of the Appendicular Skeleton

Region	Main Bones	Number of Bones
Pectoral Girdle	Clavicle, Scapula	4
Upper Limbs	Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges	60
Pelvic Girdle	Hip bones (Ilium, Ischium, Pubis), Sacrum, Coccyx	2 (hip bones only; sacrum and coccyx are part of axial skeleton but functionally included)
Lower Limbs	Femur, Tibia, Fibula, Patella, Tarsals, Metatarsals, Phalanges	60

Additional info:

• The appendicular skeleton is essential for movement and interaction with the environment, while the axial skeleton provides support and protection for vital organs.

• Differences in structure between the pectoral and pelvic girdles reflect their different functional roles: mobility versus stability.