The Skeletal System: The Appendicular Skeleton

Divisions of the Skeletal System Axial skeleton—protects and supports the internal organs Appendicular skeleton—facilitates movement The appendicular skeleton consists of 126 bones; it includes bones of the limbs and the girdles

Pectoral (Shoulder) Girdles Attach the bones of the upper limbs to the axial skeleton Each consists of 2 bones: clavicle and scapula

Clavicle Collarbone An s-shaped bone that articulates with the manubrium of the sternum and with the scapula One of the most frequently fractured bones of the body

Fig. 08.02

Scapula Shoulder blade A triangular-shaped flat bone that articulates with the clavicle The acromion is a process of the scapula that can be felt as the high point of the shoulder The glenoid cavity is a depression of the scapula that articulates with the humerus to form the shoulder joint

Upper Limbs Each upper limb has 30 bones: Humerus (1) Radius (1) Ulna (1) Carpals (8) Metacarpals (5) Phalanges (14)

Humerus Upper arm bone The longest and largest bone of the upper limb Articulates proximally with the scapula and distally at the elbow with the radius and ulna of the forearm The head articulates with the glenoid cavity of the scapula The capitulum articulates with the head of the radius; the trochlea articulates with the ulna

Radius and Ulna Long bones of the forearm The ulna is longer than the radius and is located on the “little-finger” side of the forearm The olecranon of the ulna forms the prominence of the elbow The radius is located on the thumb side of the forearm The elbow joint is formed by 2 articulations: The trochlear notch of the ulna with the trochlea of the humerus The head of the radius with the capitulum of the humerus

Carpals The wrist consists of 8 small bones called carpals These bones are arranged in two rows of four bones each In most carpal fractures, only the scaphoid carpal bone is broken

Metacarpals The palm of the hand consists of 5 long bones called metacarpals Each of these bones consists of a base, shaft, and head The metacarpals are numbered 1 through 5, starting with the thumb The “knuckles” are the heads of the metacarpals

Phalanges The long bones of the fingers (digits) There are 14 phalanges in each hand Each phalanx consists of a base, shaft, and head There are 2 phalanges in the thumb, or pollex, and 3 phalanges in each of the other four digits

Pelvic (Hip) Girdles Consist of 2 hip bones, called coxal bones These 2 bones unite anteriorly at a joint called the pubic symphysis and posteriorly with the sacrum at the sacroiliac joints The 2 coxal bones and the sacrum form the pelvis; the pelvis supports the vertebral column and pelvic organs and attaches the lower limbs to the axial skeleton In an adult, each coxal bone consists of three bones that fused together after birth: Ilium Ischium Pubis

Pelvic (Hip) Girdles (continued) The ilium is the largest and most superior of the three hip bone components; it articulates with the sacrum to form the sacroiliac joint The ischium is located inferior and posterior; the pubis is located inferior and anterior; together, they surround the obturator foramen, the largest foramen of the skeleton All three of these bones make up the acetabulum, a deep fossa that accepts the round head of the femur The two coxal bones meet anteriorly at a joint called the pubic symphysis; this joint contains a cartilage disc that gives the joint flexibility The pelvis of a female is wider and shallower than that of a male to allow for childbirth

Lower Limbs Each lower limb has 30 bones: Femur (1) Patella (1) Tibia (1) Fibula (1) Tarsals (7) Metatarsals (5) Phalanges (14)

Femur Thigh bone Longest, heaviest, and strongest bone in the body Its proximal end consists of a head that articulates with the hip bone at the acetabulum; its distal end articulates with the tibia and patella

Patella Kneecap A small, triangular bone located anterior to the knee joint It is a sesamoid bone, which develops in the tendon of the “quadriceps” muscle Articulates with the femur

Tibia and Fibula The tibia is the shinbone It is the larger, medial, weight-bearing bone of the lower leg At is proximal end, the tibia articulates with the femur and fibula; at its distal end, it articulates with the fibula and the talus bone of the ankle The fibula is the smaller bone of the lower leg It lies parallel and lateral to the tibia

Tarsals The ankle consists of 7 bones called tarsals The calcaneus is the largest and strongest tarsal bone; it is located in the posterior heel part of the foot The talus is the uppermost tarsal bone; it articulates with the fibula and tibia

Metatarsals The main part of the foot consists of 5 long bones called metatarsals Each of these bones consists of a base, shaft, and head The metatarsals are numbered 1 through 5, from the medial to lateral position

Phalanges The long bones of the toes There are 14 phalanges on each foot Each phalanx consists of a base, shaft, and head There are 2 phalanges in the big toe, or hallux, and 3 phalanges in each of the other four digits