The Appendicular Skeleton

THE SKELETAL SYSTEMThe Appendicular Skeleton

• 2 pairs of limbs and 2 girdles• Pectoral (shoulder) girdle attaches upper limbs• Pelvic (hip) girdle secures lower limbs• 3-Segmented limbs– Upper = arm

• Humerus• Radius & Ulna• Hand

– Lower = leg• Femur• Tibia & Fibula• Foot

Pectoral Girdle

(Shoulder Girdle)

• Clavicle – anterior: collar bone• Scapula – posterior: shoulder blade

Scapulae: triangular, paired, but don’t connect in back (adds thoracic flexibility)

Upper extremity

• Arm or Brachium = upper arm– Between shoulder and

elbow (humerus)• Forearm or

Antebrachium– Radius & ulna

• Hand includes:– Wrist (carpus)– Palm (metacarpus)– Fingers (phalanges)

Arm– Humerus is the only

bone– Head of humerus fits

into scapula– Distal & medially,

articulates with the ulna– Distal & laterally

articulates with the radius

Arm

Right humerus,

anterior view

Right humerus, posterior view

Forearm

• 2 bones: articulate with each other proximally and distally

• Interosseous membrane between them

• Ulna– Olecranon process hinges with the

humerus forming elbow• Radius

– Contributes to wrist joint– Styloid process anchors a ligament

to wrist (thumb side)

Radius is thinner proximally, like a spool of thread, and wide distally; ulna is slightly longer

Right forearm bones, anterior view

Right forearm bones, posterior view

In the anatomical position, the radius is lateral (thumb side); with pronation the palm faces posteriorly and the bones cross

Left forearm

Prone: Turning the hand so that the palm is down Suppine: Turning the hand so that the palm is up

Anatomical position

prone

pronation moves the forearm into the prone position and supination moves it back to the anatomical position

proximal ulna

Proximal and distal joints of the forearm

Hand• Proximal is “wrist” – 8 carpal bones• Palm of hand - 5 metacarpals• Fingers (or digits) consist of miniature long bones called

phalanges: thumb (“pollex”) has 2; fingers have 3: proximal, middle, distal

Right hand, 2 views:

Pelvic Girdle (Hip Girdle)

• Strongly attached to axial skeleton (sacrum)• Deep sockets• More stable than pectoral (shoulder) girdle• Less freedom of movement• Made up of the paired hip bones– “Bony pelvis” is basin-like structure: hip bones plus

the axial sacrum and coccyx

Hip bone (os coxae): 3 separate bones in childhood which fuse

• Ilium

• Ischium

• Pubis

Ilium• Forms part of

hip socket which receives ball-shaped head of femur

ilium

ilium

Hip bones with labels

Pelvis and childbearing• Male/female differences– Large & heavy vs light & delicate– Heart shaped pelvic inlet vs oval– Narrow deep true pelvis vs wide & shallow– Narrow outlet vs wide– Less than 90 degree pubic arch vs more than 90 degree

• Birth canal changes shape as baby descends: head turns ¼– Higher: pelvic inlet (brim) - side to side largest– Lower: pelvic outlet - largest in AP direction

Male vs. Female Pelvis

Lower limb

• Thigh: femur

• Leg (lower leg)– Tibia– Fibula

• Foot

Thigh

• Femur is largest, longest and strongest bone in the body

• Head fits in socket of pelvis• Neck is weakest

Right femur, anterior view

Right femur, posterior view

Leg

• Tibia: shin bone• Fibula– Interosseous membrane

Right lower leg, anterior view

Foot• Tarsus: 7 tarsal bones– Talus: articulates with tibia

and fibula anteriorly and calcaneus posteriorly

– Calcaneus: heel bone– Smaller cuboid, navicular,

and 3 cunieforms (medial, intermediate and lateral)

• 5 metatarsals• 14 phalanges– Great toe is hallux

Right foot, superior (dorsal) view and inferior (plantar) view

Right foot, lateral and medial views

Arches