Skeletal Notes - Part 5

Bony Thorax

The bony thorax is made up of the:1. Sternum2. Ribs3. Thoracic vertebrae

Often called the “thoracic cage.” It forms a protective,

cone-shaped cage of slender bones around the organs of the thoracic cavity (heart, lungs, and major blood vessels).

Sternum

The sternum (breastbone) is a typical flat bone and the result of the fusion of three bones:

1. Manubrium2. Body3. Xiphoid Process

The sternum is attached to the first 7 pairs of ribs.

Ribs

Twelve pairs of ribs form the walls of the thoracic cage. Contrary to popular

misconception, males do not have one less rib than females!

All the ribs articulate with the vertebral column posteriorly and then curve downward toward the anterior body surface.

Ribs

True Ribs – Attach directly to the sternum by costal cartilages; The first seven pairs.

False Ribs – Either attach indirectly to the sternum or are not attached to the sternum at all; The next five pairs of ribs. Floating Ribs – Lack a

sternal attachment; Last two pairs of the false ribs.

Intercostal Spaces

Intercostal Spaces - Spaces between the ribs. Are filled with the

intercostal muscles that aid in breathing.

Appendicular Skeleton

It is composed of 126 bones of the limbs and the pectoral and pelvic girdles, which attach the limbs to the axial skeletal.

Bones of the Shoulder Girdle

Each shoulder girdle (pectoral girdle) consists of two bones:

1. Clavicle2. Scapula

Clavicle

Clavicle – Collarbone; slender doubly curved bone. Attaches:

To the sternum medially To the scapula laterally, where it

helps to form the shoulder joint. Acts as a brace to hold the arm

away from the top of the thorax and helps prevent shoulder dislocation. When the clavicle is broken, the

whole shoulder region caves in medially, which shows how important its bracing function is.

Scapulae

Scapulae – Shoulder blades. Not directly attached to the axial skeleton; is

loosely held in place by trunk muscles. Each scapula has a flattened body and two

important processes:1. Acromion – The enlarged end of

the spine of the scapula.

• The acromion connects with the clavicle laterally at the acromio- clavicular joint.

2. Coracoid Process – Beaklike process.• The coracoid process points over

the top of the shoulder and anchors some of the muscles of the arm.

The Shoulder Girdle

Is very light and allows the upper limb to have exceptional free movement because:

1. Attaches to the axial skeleton at only one point – the sternoclavicular joint.

2. The loose attachment of the scapula allows it to slide back and forth against the thorax as muscles act.

3. The glenoid cavity is shallow, and the shoulder joint is poorly reinforced by ligaments.

However, this exceptional flexibility also has a drawback, the shoulder girdle is easily dislocated.

Bones of the Upper Limbs

30 separate bones form the skeletal framework of each upper limb.

They form the foundations of the arm, forearm, and hand.

Arm

The arm is formed by a single bone, the humerus, which is a typical long bone. At its proximal end is a

rounded head that fits into the shallow glenoid cavity of the scapula.

Forearm

Two bones form the skeleton of the forearm:

1. Radius – The lateral bone, when the body is in anatomical position; on the thumb side of the forearm.

2. Ulna – The medial bone, when the body is in anatomical position; on the little finger side of the forearm.

Radius and Ulna

Both proximally and distally, the radius and ulna articulate at small radioulnar joints.

The two bones are connected along their entire length by the flexible interosseous membrane.

Hand

The skeleton of the hand consists of:

1. The carpals2. The metacarpals3. The phalanges

Hand: Carpals

The eight carpal bones form the part of the hand called the carpus or the wrist. The carpal bones are

arranged in two irregular rows of four bones each.

The carpals are bound together by ligaments that restrict movements between them.

Hand: Metacarpals

The palm of the hand consists of the metacarpals. The metacarpals are

numbered 1-5 from the thumb side of the hand toward the little finger.

When the fist is clenched, the heads of the metacarpals become obvious as the “knuckles.”

Hand: Phalanges

The phalanges are the bones of the fingers. Each hand contains 14

phalanges. There are three

phalanges in each finger (proximal, middle, and distal) except for the thumb, which has only two (proximal and distal).