Chapter 8: The Skeletal System – The Appendicular Skeleton

Introduction to the Appendicular Skeleton

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.

• Main regions: Upper limb and lower limb

• Girdles: Pectoral (shoulder) girdle and pelvic (hip) girdle

Skeleton of the Upper Limb

Overview of the Upper Limb

The upper limb is composed of 30 bones, divided into two main regions: the pectoral girdle and the free part (arm, forearm, and hand).

• Pectoral (shoulder) girdle: 2 bones (scapula and clavicle)

• Free part: 30 bones (humerus, ulna, radius, carpals, metacarpals, phalanges)

Pectoral Girdle

Clavicle

The clavicle is an S-shaped bone that lies anteriorly and superiorly to the thorax. It is one of the most frequently broken bones in the body.

• Function: Acts as a strut to keep the scapula in position

• Location: Connects the upper limb to the trunk

Scapula

The scapula, or shoulder blade, is a triangular-shaped bone that articulates with both the humerus and the clavicle.

• Function: Provides attachment for muscles and forms the socket for the shoulder joint

Free Part of the Upper Limb

• Humerus: The single bone of the arm, longest and largest of the upper limb

• Ulna: Located medially (pinky side) in the forearm

• Radius: Located laterally (thumb side) in the forearm

• Carpals: 8 wrist bones

• Metacarpals: 5 bones forming the palm

• Phalanges: 14 bones in the fingers (3 in each finger, 2 in the thumb)

Skeleton of the Hand

Carpal Bones

The wrist contains 8 carpal bones arranged in two rows.

• Proximal row: Scaphoid, lunate, triquetrum, pisiform

• Distal row: Trapezium, trapezoid, capitate, hamate

Metacarpals and Phalanges

• Metacarpals: Numbered I-V from thumb to little finger

• Phalanges: 14 total; thumb (pollex) has 2, other fingers have 3 each

Skeleton of the Lower Limb

Overview of the Lower Limb

The lower limb consists of 30 bones, divided into the pelvic girdle and the free part (thigh, leg, and foot).

• Pelvic (hip) girdle: 2 bones (coxal bones)

• Free part: 30 bones (femur, patella, tibia, fibula, tarsals, metatarsals, phalanges)

Pelvic (Hip) Girdle

The pelvic girdle is formed by two coxal bones, each consisting of three fused bones: ilium, ischium, and pubis.

• Ilium: Superior part, largest

• Ischium: Inferior and posterior part

• Pubis: Inferior and anterior part

Comparison of Male and Female Pelves

Skeleton of the Thigh

• Femur: Longest, heaviest, and strongest bone in the body

• Patella: Largest sesamoid bone, protects the knee joint

Skeleton of the Leg

• Tibia: Shin bone, larger and weight-bearing

• Fibula: Smaller, non-weight-bearing

Skeleton of the Foot

• Tarsals: 7 bones (talus, calcaneus, navicular, cuboid, 3 cuneiforms)

• Metatarsals: 5 bones

• Phalanges: 14 bones (big toe is the hallux)

Arches of the Foot

The foot has three arches that support body weight, provide spring and leverage, and help maintain balance during walking.

• Medial longitudinal arch

• Lateral longitudinal arch

• Transverse arch

Key Terms and Definitions

• Appendicular skeleton: Bones of the limbs and girdles

• Pectoral girdle: Shoulder girdle (scapula and clavicle)

• Pelvic girdle: Hip girdle (coxal bones)

• Sesamoid bone: A bone embedded within a tendon (e.g., patella)

• Phalanges: Bones of the fingers and toes

Summary Table: Major Bones of the Appendicular Skeleton

Additional info:

• All bones listed are paired except for the patella and some tarsals/carpals.

• The appendicular skeleton is crucial for locomotion and manipulation of objects.