Appendicular Skeleton: Pectoral Girdle

• The appendicular skeleton includes the pectoral and pelvic girdles, and upper and lower limbs.
• The pectoral girdle attaches the upper limbs to the trunk.
• The pelvic girdle attaches the lower limbs to the trunk.
• Upper and lower limbs differ in function.
• Still, they share the same structural plan.

The Pectoral Girdle

• The pectoral girdle consists of the clavicle and the scapula.
• The pectoral girdle provides attachment for many muscles that move the upper limb.
• The girdle is very light and allows for mobile upper limbs.
• Only the clavicle articulates with the axial skeleton.
• The shoulder joint’s socket (glenoid cavity) is shallow, which allows for flexibility but reduces stability.

Clavicles

• Clavicles extend horizontally across the superior thorax.
• The sternal end articulates with the manubrium.
• The acromial end articulates with the scapula.
• Clavicles provide attachment for muscles, hold the scapulae and arms laterally, and transmit compression forces from the upper limbs to the axial skeleton.

Scapulae

• The scapulae lie on the dorsal surface of the rib cage and are located between ribs 2-7.
• Scapulae have three borders: superior, medial (vertebral), and lateral (axillary).
• Scapulae have three angles: lateral, superior, and inferior.

The Upper Limb

• Each upper limb has 30 bones grouped into regions: arm, forearm, and hand.

Arm

• The arm refers to the region of the upper limb between the shoulder and elbow.
• The humerus is the only bone of the arm.
• It is the longest and strongest bone of the upper limb.
• The humerus articulates with the scapula at the shoulder and with the radius and ulna at the elbow.
• Many structures of the humerus provide sites for muscle attachment.
• Other structures of the humerus provide articulation sites for other bones.

Forearm

• The forearm is formed from the radius and ulna.
• The proximal ends articulate with the humerus, and the distal ends articulate with carpals.
• The radius and ulna articulate with each other at proximal and distal radioulnar joints.
• The interosseous membrane interconnects the radius and ulna.
• When in anatomical position, the radius is lateral and the ulna is medial.

Ulna

• The ulna is the main bone responsible for forming the elbow joint with the humerus.
• A hinge joint allows the forearm to bend on arm.
• The distal end is separated from carpals by fibrocartilage and plays little to no role in hand movement.

Radius

• The superior surface of the head of the radius articulates with the capitulum.
• Medially, the head of the radius articulates with the radial notch of the ulna.
• The radius contributes heavily to the wrist joint.
• The Distal radius articulates with carpal bones, when the radius moves, the hand moves with it.

Hand

• The hand includes the following bones: carpus (wrist), metacarpals (palm), and phalanges (fingers).

Carpus

• What forms the true wrist–the proximal region of the hand.
• Gliding movements occur between carpals.
• The carpus is composed of eight marble-sized bones arranged in two irregular rows.
• The proximal row from lateral to medial consists of the scaphoid, lunate, triquetrium, and pisiform.
• The distal row from lateral to medial consists of the trapezium, trapezoid, capitate, and hamate.
• A mnemonic to help remember carpals: "Sally left the party to take Carmen home."

Metacarpus

• Five metacarpals radiate distally from the wrist and form the palm.
• The metacarpals are numbered 1–5, beginning with the pollex (thumb).
• Metacarpals articulate proximally with the distal row of carpals and distally with the proximal phalanges.

Phalanges

• Except for the thumb, each finger has three phalanges: proximal, middle, and distal.

Pelvic Girdle

• The pelvic girdle attaches the lower limbs to the spine and supports visceral organs.
• It attaches to the axial skeleton by strong ligaments.
• The acetabulum is a deep cup that holds the head of the femur.
• Lower limbs have less freedom of movement but are more stable than the arm.

Bones of the Pelvic Girdle

• The pelvic girdle consists of paired hip bones (coxal bones) that unite anteriorly and articulate posteriorly with the sacrum.
• The hip bone forms by the fusion of ilium, ischium, and pubis.

Ilium

• The ilium is a large, flaring bone that forms the superior region of the coxal bone and serves as a site of attachment for many muscles.
• Articulation with the sacrum forms the sacroiliac joint.

Ischium

• The ischium forms the posteroinferior region of the coxal bone and anteriorly joins the pubis.
• Ischial tuberosities are the strongest part of the hip bone.

Pubis

• The pubis forms the anterior region of the coxal bone and lies horizontally in anatomical position.
• The two pubic bones are joined by fibrocartilage at the midline, forming the pubic symphysis.
• The pubic arch is inferior to the pubic symphysis where the angle helps distinguish male from female pelves.

True and False Pelves

• The bony pelvis is divided into two regions: false (greater) pelvis bounded by alae of the iliac bones, and true (lesser) pelvis inferior to the pelvic brim.
• The true pelvis forms a bowl containing the pelvic organs.

Pelvic Structures and Childbearing

• Major differences exist between male and female pelves.
• The female pelvis is adapted for childbearing, being lighter, wider, and shallower than the male pelvis.
• It provides more room in the true pelvis.

The Lower Limb

• The lower limb carries the entire weight of the erect body.
• Bones of the lower limb are thicker and stronger than those of upper limb.
• It is divided into three segments: thigh, leg, and foot.

Thigh

• The thigh is the region of the lower limb between the hip and the knee.
• The femur is the single bone of the thigh, being the longest and strongest bone of the body.
• The ball-shaped head articulates with the acetabulum.

Leg

• The leg refers to the region of the lower limb between the knee and the ankle.
• The leg is composed of the tibia and fibula.
• The tibia is the more massive medial bone of the leg that receives the body's weight from the femur.
• The fibula is the stick-like lateral bone of the leg.
• The interosseous membrane connects the tibia and fibula.
• The tibia articulates with the femur at the superior end, forming the knee joint.
• The tibia articulates with the talus at the inferior end, forming the ankle joint.
• The fibula does not contribute to the knee joint but stabilizes the ankle joint.

The Foot

• The foot is composed of the tarsus, metatarsus, and the phalanges.
• Important functions of the foot Includes supports body weight, acts as a lever to propel body forward when walking, and provides segmentation that makes the foot pliable and adapted to uneven ground.

Tarsus

• It makes up the posterior half of the foot and contains seven bones called tarsals.
• Body weight is primarily borne by the talus and calcaneus.
• The trochlea of the talus is the site of articulation with the tibia.
• Other tarsals are: Cuboid and navicular, Medial, intermediate, and lateral cuneiforms

Metatarsus

• The metatarsus Consists of five small long bones called metatarsals and are Numbered 1–5 beginning with the hallux (great toe).
• The first metatarsal supports body weight.

Phalanges of the Toes

• The phalanges consist of 14 phalanges of the toes with a structure and arrangement are similar to phalanges of fingers.
• the toes Are Smaller and less nimble than those of the fingers
• The great toe which has two, except for the toes have each toes had three phalanges: Proximal, middle, and distal.