Study Guide: The Appendicular Skeleton (Chapter 7)

The Appendicular Skeleton

Overview of the Appendicular Skeleton

The appendicular skeleton consists of the bones that support the limbs and enable movement. It is divided into the pectoral girdle, upper limbs, pelvic girdle, and lower limbs. These structures are essential for locomotion and manipulation of the environment.

• Pectoral girdle: Clavicle and scapulae

• Upper limbs: Humerus, ulna, radius, carpals, metacarpals, phalanges

• Pelvic girdle: Coxal bones (ilium, ischium, pubis)

• Lower limbs: Femur, tibia, fibula, patella, tarsals, metatarsals, phalanges

Axial vs. Appendicular Skeleton

The human skeleton is divided into two main parts: the axial skeleton and the appendicular skeleton. The axial skeleton consists of 80 bones, while the appendicular skeleton consists of 126 bones.

• Axial skeleton: Skull, vertebral column, rib cage

• Appendicular skeleton: Limbs and girdles

Region	Number of Bones
Axial Skeleton	80
Appendicular Skeleton	126
Pectoral Girdle	4
Upper Limbs	60
Pelvic Girdle	2
Lower Limbs	60

The Pectoral Girdle and Upper Limb

The Clavicle

The clavicle, or collarbone, is a slender, S-shaped bone that connects the pectoral girdle to the axial skeleton. It has two ends:

• Sternal end: Medial; articulates with the sternum

• Acromial end: Lateral; articulates with the scapula

The Scapula

The scapula, or shoulder blade, is a flat, triangular bone that forms the socket of the shoulder joint. The glenoid cavity is the site of articulation with the humerus.

• Key features: Acromion, coracoid process, glenoid cavity, spine, borders (superior, medial, lateral), angles (superior, inferior, lateral)

The Upper Limb Bones

The upper limb consists of the humerus, ulna, radius, carpal bones, metacarpals, and phalanges. These bones allow for a wide range of motion and dexterity.

• Humerus: The bone of the upper arm

• Ulna and Radius: Forearm bones

• Carpal bones: Eight bones of the wrist

• Metacarpals: Five bones of the palm

• Phalanges: Fourteen bones of the fingers

The Humerus

The humerus is the largest bone of the upper limb. It articulates proximally with the scapula and distally with the radius and ulna.

• Proximal structures: Head, greater and lesser tubercles, anatomical and surgical necks, intertubercular sulcus

• Shaft: Deltoid tuberosity, radial groove

• Distal structures: Capitulum, trochlea, epicondyles, fossae (radial, coronoid, olecranon)

The Ulna and Radius

The ulna and radius are the two bones of the forearm. The ulna is medial, and the radius is lateral in anatomical position. They are connected by the interosseous membrane.

• Ulna: Olecranon, trochlear notch, radial notch, ulnar styloid process

• Radius: Head, radial tuberosity, radial styloid process

• Interosseous membrane: Fibrous sheet between the ulna and radius

The Carpal Bones

The wrist contains eight carpal bones, arranged in two rows:

• Proximal row: Scaphoid, lunate, triquetrum, pisiform

• Distal row: Trapezium, trapezoid, capitate, hamate

The Metacarpals and Phalanges

The metacarpals are numbered I to V, starting from the thumb (pollex). Each hand has 14 phalanges: proximal, middle, and distal for each finger except the thumb, which has only proximal and distal phalanges.

• Metacarpal I: Associated with the thumb

• Phalanges: Proximal, middle, distal (thumb lacks middle phalanx)

The Pelvic Girdle and Lower Limb

The Pelvic Girdle

The pelvic girdle consists of two coxal (hip) bones, each formed by the fusion of the ilium, ischium, and pubis. It supports the weight of the upper body and protects pelvic organs.

• Ilium: Iliac crest, iliac fossa, anterior/posterior superior/inferior iliac spines

• Ischium: Ischial tuberosity, ischial spine, lesser sciatic notch

• Pubis: Superior/inferior pubic ramus, pubic symphysis

• Acetabulum: Socket for the femur

• Obturator foramen: Large opening for nerves and blood vessels

The Pelvis

The pelvis is formed by the two coxal bones, sacrum, and coccyx. It is divided into the greater (false) pelvis and lesser (true) pelvis. The pelvic inlet and outlet are important for childbirth.

• Greater pelvis: Area between iliac crests

• Lesser pelvis: Area below the iliopectineal line

• Pelvic inlet: Superior opening

• Pelvic outlet: Inferior opening

Male vs. Female Pelvis

The female pelvis is adapted for childbirth, with a wider pelvic inlet and outlet, less curvature of the sacrum and coccyx, and a broader pubic angle.

• Pelvic outlet: Larger in females

• Sacrum curve: Less in females

• Pelvic inlet: Wider in females

• Pubic angle: Greater than 100º in females, less than 90º in males

The Lower Limb Bones

The lower limb consists of the femur, patella, tibia, fibula, tarsal bones, metatarsals, and phalanges. These bones support the body and enable movement.

• Femur: Thigh bone, largest bone in the body

• Patella: Sesamoid bone protecting the knee joint

• Tibia: Medial bone of the leg

• Fibula: Lateral bone of the leg

• Tarsal bones: Seven bones of the ankle

• Metatarsals: Five bones of the foot

• Phalanges: Fourteen bones of the toes

The Femur

The femur is the longest and strongest bone in the body. It articulates proximally with the pelvis and distally with the tibia and patella.

• Proximal structures: Head, fovea, neck, greater and lesser trochanters, intertrochanteric line and crest

• Distal structures: Medial and lateral condyles, epicondyles, intercondylar fossa, popliteal surface, patellar surface

The Patella

The patella is a large sesamoid bone that protects the knee joint. Its anterior surface is rough for tendon attachment, while the posterior surface has concave facets for articulation with the femoral condyles.

• Apex: Pointed end

• Base: Broad end

• Medial and lateral facets: Articulate with femoral condyles

The Tibia and Fibula

The tibia is the main weight-bearing bone of the leg, located medially. The fibula is lateral and provides muscle attachment and stability to the ankle.

• Tibia: Tibial tuberosity, medial and lateral condyles, anterior margin, interosseous border, medial malleolus

• Fibula: Head, lateral malleolus

The Tarsal Bones

The ankle contains seven tarsal bones:

• Calcaneus: Heel bone

• Talus: Articulates with tibia and fibula

• Navicular, cuboid, medial/intermediate/lateral cuneiform bones: Contribute to the structure of the foot

The Metatarsals and Phalanges

The metatarsals are numbered I to V, starting from the hallux (great toe). Each foot has 14 phalanges: proximal, middle, and distal for each toe except the hallux, which has only proximal and distal phalanges.

• Metatarsal I: Associated with the hallux

• Phalanges: Proximal, middle, distal (hallux lacks middle phalanx)

Arches of the Foot

The foot has two main arches: the longitudinal arch and the transverse arch. These arches help distribute body weight and provide springiness to the step.

• Longitudinal arch: Runs from heel to toe

• Transverse arch: Runs across the foot