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The sternum    , or breastbone, is a long, flat bone located at the anterior of the chest. It is formed from three bones that fuse in the adult. The ribs are 12 pairs of long, curved bones that attach to the thoracic vertebrae and curve toward the front of the body, forming the ribcage. Costal cartilages connect the anterior ends of the ribs to the sternum, with the exception of rib pairs 11 and 12, which are free-floating ribs.

Illustration shows the rib cage and the sternum, which is the bone in the front and center of the upper body. The rib bones, which end about three quarters of the way around the body, do not connect directly to the sternum; instead, costal cartilage connects the rib bones to the sternum.
The thoracic cage, or rib cage, protects the heart and the lungs. (credit: modification of work by NCI, NIH)

Human appendicular skeleton

The appendicular skeleton    is composed of the bones of the upper limbs (which function to grasp and manipulate objects) and the lower limbs (which permit locomotion). It also includes the pectoral girdle, or shoulder girdle, that attaches the upper limbs to the body, and the pelvic girdle that attaches the lower limbs to the body ( [link] ).

Illustration shows the appendicular skeleton, which consists of arms, legs, shoulder bones, and the pelvic girdle.
The appendicular skeleton is composed of the bones of the pectoral limbs (arm, forearm, hand), the pelvic limbs (thigh, leg, foot), the pectoral girdle, and the pelvic girdle. (credit: modification of work by Mariana Ruiz Villareal)

The pectoral girdle

The pectoral girdle    bones provide the points of attachment of the upper limbs to the axial skeleton. The human pectoral girdle consists of the clavicle (or collarbone) in the anterior, and the scapula (or shoulder blades) in the posterior ( [link] ).

Illustration shows the pectoral girdles of the shoulder. Each girdle consists of a long, thin clavicle that runs from the sternum to the arm and a flat, triangular scapula that extends down from the clavicle. Viewed from the back, the upper part of the scapula has a prominent protrusion, called a spine.
(a) The pectoral girdle in primates consists of the clavicles and scapulae. (b) The posterior view reveals the spine of the scapula to which muscle attaches.

The clavicles are S-shaped bones that position the arms on the body. The clavicles lie horizontally across the front of the thorax (chest) just above the first rib. These bones are fairly fragile and are susceptible to fractures. For example, a fall with the arms outstretched causes the force to be transmitted to the clavicles, which can break if the force is excessive. The clavicle articulates with the sternum and the scapula.

The scapulae are flat, triangular bones that are located at the back of the pectoral girdle. They support the muscles crossing the shoulder joint. A ridge, called the spine, runs across the back of the scapula and can easily be felt through the skin ( [link] ). The spine of the scapula is a good example of a bony protrusion that facilitates a broad area of attachment for muscles to bone.

The upper limb

The upper limb contains 30 bones in three regions: the arm (shoulder to elbow), the forearm (ulna and radius), and the wrist and hand ( [link] ).

Illustration shows a skeletal human arm. The humerus is the bone of the upper arm. The radius is the thick bone in the forearm, and the ulna is the thin bone. The carpals are the bones of the wrist, the metacarpals are bones of the hand, and phalanges are bones of the fingers.
The upper limb consists of the humerus of the upper arm, the radius and ulna of the forearm, eight bones of the carpus, five bones of the metacarpus, and 14 bones of the phalanges.

An articulation    is any place at which two bones are joined. The humerus    is the largest and longest bone of the upper limb and the only bone of the arm. It articulates with the scapula at the shoulder and with the forearm at the elbow. The forearm    extends from the elbow to the wrist and consists of two bones: the ulna and the radius. The radius    is located along the lateral (thumb) side of the forearm and articulates with the humerus at the elbow. The ulna    is located on the medial aspect (pinky-finger side) of the forearm. It is longer than the radius. The ulna articulates with the humerus at the elbow. The radius and ulna also articulate with the carpal bones and with each other, which in vertebrates enables a variable degree of rotation of the carpus with respect to the long axis of the limb. The hand includes the eight bones of the carpus    (wrist), the five bones of the metacarpus    (palm), and the 14 bones of the phalanges (digits). Each digit consists of three phalanges, except for the thumb, when present, which has only two.

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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