Appendicular Skeleton: Structure and Components

Appendicular Skeleton

Introduction

The appendicular skeleton is one of the two major divisions of the human skeletal system, consisting of the bones that support the appendages (limbs). It is essential for movement and interaction with the environment.

• Pectoral girdle: Composed of the shoulder bones, it connects the upper limbs to the axial skeleton.

• Upper limbs: Includes the bones of the arms, forearms, wrists, and hands.

• Pelvic girdle: Formed by the hip bones, it connects the lower limbs to the axial skeleton and supports the weight of the body.

• Lower limbs: Includes the bones of the thighs, legs, ankles, and feet.

Overview of Appendicular Skeleton Components

The appendicular skeleton consists of 126 bones in the adult human body. These bones are organized into the pectoral girdle, upper limbs, pelvic girdle, and lower limbs.

• Pectoral girdle: 4 bones (2 clavicles, 2 scapulae)

• Upper limbs: 60 bones (2 humeri, 2 radii, 2 ulnae, 16 carpals, 10 metacarpals, 28 phalanges)

• Pelvic girdle: 2 bones (hip bones, each formed by fusion of ilium, ischium, and pubis)

• Lower limbs: 60 bones (2 femora, 2 patellae, 2 tibiae, 2 fibulae, 14 tarsals, 10 metatarsals, 28 phalanges)

Example: The diagram below (from the original material) shows the anterior and posterior views of the skeleton, highlighting the appendicular components and the number of bones in each category.

Pectoral Girdle and Upper Limb

Pectoral Girdle

The pectoral girdle anchors the upper limb to the trunk and provides attachment points for muscles that move the shoulder and arm.

• Clavicle: Also known as the collarbone, it is a long bone that serves as a strut between the shoulder blade and the sternum.

• Scapula: Also known as the shoulder blade, it is a flat, triangular bone that provides attachment for several muscles and articulates with the clavicle and humerus.

Definition: The pectoral girdle consists of two bones on each side: the clavicle (anteriorly) and the scapula (posteriorly).

Upper Limb

The upper limb is specialized for mobility and manipulation. It consists of several bones organized into the arm, forearm, wrist, and hand.

• Humerus: The single bone of the upper arm, articulating with the scapula at the shoulder and with the radius and ulna at the elbow.

• Radius: One of the two bones of the forearm, located on the lateral (thumb) side.

• Ulna: The other bone of the forearm, located on the medial (little finger) side.

• Carpals: Eight small bones that make up the wrist.

• Metacarpals: Five bones that form the palm of the hand.

• Pollex and other digits: The pollex is the thumb, which has two phalanges; the other fingers each have three phalanges.

Example: The humerus articulates proximally with the scapula at the glenohumeral joint and distally with the radius and ulna at the elbow joint.

Summary Table: Major Bones of the Appendicular Skeleton

Region	Main Bones	Number (per side)
Pectoral Girdle	Clavicle, Scapula	2
Upper Limb	Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges	15
Pelvic Girdle	Hip bone (ilium, ischium, pubis)	1
Lower Limb	Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges	15

Additional info: The appendicular skeleton is crucial for locomotion and manipulation of objects, and its structure reflects the functional demands placed on the limbs.