The Skeletal System 10/3/25

Pectoral Girdle

Pectoral girdle – clavicle and scapula; supports 30 bones that make up upper limb; all are components of appendicular skeleton

• Each clavicle end is distinct and palpable through skin

Sternal end

articulates medially with manubrium at sternoclavicular joint

Acromial end

articulates laterally with acromion process of scapula at acromioclavicular joint; conoid tubercle provides site for attachment of ligaments near end

Triangular scapula

Triangular scapula sits on posterosuperior rib cage between second and seventh ribs; body is largest section; has three borders: medial, lateral, and superior

• Coracoid process – hook-shaped projection on anterior surface

• Subscapular fossa – inferior to coracoid process; provides attachment site for subscapularis muscle

• Glenoid cavity – shallow indentation on lateral surface; articulates with humerus in shoulder joint

• Spine – posterior ridge of bone; crosses from medial to lateral along superior scapula; terminates as acromion at acromioclavicular joint (AC)

• Supraspinous fossa – superior to spine; infraspinous fossa is inferior

The Humerus

Humerus – largest and strongest bone of upper limb; only bone in arm (brachium); consists of two epiphyses; articulate with other bones and long diaphysis

Features associated with humeral articulation with ulna and radius at elbow joint:

• Capitulum – spherical knob on anterior and lateral aspect of distal epiphysis

• Trochlea – spool-shaped knob on anterior and medial aspect of distal epiphysis

• Lateral radial fossa and medial coronoid fossa – small indentations just proximal to capitulum and trochlea

• Olecranon fossa – deep indentation on posterior aspect of distal epiphysis; continuation of trochlea

Bones of forearm (antebrachium)

Lateral radius and medial ulna; held to one another by fibrous interosseous membrane

Radius, Ulna

• Radius – narrow proximally; progressively enlarges distally

• Proximal epiphysis (radial head) – round and flattened structure; articulates with capitulum of humerus at elbow joint and ulna at proximal radioulnar joint

• Radial neck – distal to head, ends at radial tuberosity; on medial aspect of radius; attachment site for biceps brachii muscle

• Ulna – widest at proximal epiphysis; progressively narrows as it travels distally

Bones of the Wrist: Carpals

• Wrist (carpus) – eight short bones (carpals) arranged in two rows containing four bones each

• Hand (manus) – Five long bones (metacarpals)

Bones of the Pelvic Girdle and Lower Limb

• Pelvis and bones of pelvic girdle and lower limbs complete appendicular skeleton Hipbones or coxal bones (also known as os coxae) make up pelvic girdle

• Articulates with sacrum (component of axial skeleton)

Each coxal bone is three fused bones: ilium, ischium, and pubis

• All contribute to acetabulum; deep socket on lateral aspect of coxal bone ; head of femur articulates with acetabulum at hip joint

• Ilium and pubis also contribute to obturator foramen; opening in each coxal bone, through which nerves and blood vessels travel

Ilium

forms superior portion of coxal bone

Ischium

ischial body and ramus; forms C-shaped posteroinferior portion of coxal bone

Pubis

smallest coxal bone; three parts that approximate C-shape

Female vs Male pelvis

Female Pelvis:

Anterior view

• Wide greater pelvis

• Wider, shorter sacrum

• Acetabula farther apart

• Pelvic inlet oval shape

• Pubic arch 90-100 degree angle

Inferior view

• Ischial tuberosities point laterally

• Pelvic outlet wide

• Sacrum wider

Male Pelvis:

Anterior view

• Narrow greater pelvis

• narrower, longer sacrum

• Acetabula closer together

• Pelvic inlet heart shape

• Pubic arch 60-70 degree angle

Inferior view

• Ischial tuberosities Point medially

• Pelvic outlet narrow

• Sacrum narrower

The femur and patella

• Femur – largest and strongest bone in body and only bone in thigh

• Proximal epiphysis features prominent spherical head; articulates with acetabulum at hip joint

  • Fovea capitis – small pit in center of head where small ligament attaches to stabilize joint

• Triangular patella (kneecap) articulates with patellar surface on femur

• Sesamoid bone located within tendon of anterior thigh muscle

  • Patellar ligament – distal continuation of this tendon; inserts into tibia; secures bone over anterior knee

Tibia, Fibula

bones of leg; connected by interosseous membrane; articulate with one another at proximal and distal tibiofibular joints

• Fibula – smaller lateral bone of leg, bears only one-sixth weight of tibia

Tarsals, Metatarsals

• Tarsals – Seven short bones make up ankle region; connects leg to foot

• Metatarsals, numbered I-V from medial to lateral, have proximal base, middle shaft and distal head

Bones of foot don’t normally lie flat on ground (arched)

three arches supported by ligaments and muscles help support and distribute body weight during movement