The thoracic cavity

This is the area of the body enclosed by the ribs, providing protection for the heart and lungs.

Essential parts contained within this cavity include:

• 12 thoracic vertebrae.

Manubrium

Xiphoid process

Ribs i=J

Manubrium

Xiphoid process

Ribs

Thoracic vertebrae

Body of sternum

Costal cartilage

Fig 3.6 The thoracic cavity The sternum

This is commonly referred to as the breast bone and is a flat bone lying just beneath the skin in the centre of the chest. The sternum is divided into three parts:

• manubrium, the top section

• main body, the middle section

• xiphoid process, the bottom section.

The top section of the sternum articulates with the clavicle and the first rib. The middle section articulates with the costal cartilages that link the ribs to the sternum. The bottom section provides a point of attachment for the muscles of the diaphragm and the abdominal wall.

The ribs

There are 12 pairs of ribs. They articulate posteriorly with the thoracic vertebrae. Anteriorly, the first ten pairs attach to the sternum via the costal cartilages, the first seven directly (known as the true ribs), the remaining three indirectly (known as the false ribs). The last two ribs have no anterior attachment and are called the floating ribs.

The appendicular skeleton

This consists of the shoulder girdle, the bones of the upper and lower limbs and the pelvic girdle.

The shoulder girdle

The shoulder girdle connects the upper limbs with the thorax and consists of four bones - two scapula and two clavicle.

The scapula is a large flat bone, triangular in outline which forms the posterior part of the shoulder girdle. It is located between the second and the seventh rib. The scapula articulates with the clavicle and the humerus and serves as a point of muscle attachment which connects the shoulder girdle with the trunk and upper limbs.

The clavicle is a long slender bone with a double curve. It forms the anterior portion of the shoulder girdle. At its medial end it articulates with

Cervical vertebrae

Clavicle (collar bone)

Scapula

(shoulder blade)

Sternum

Humerus

Ribs

Cervical vertebrae

Clavicle (collar bone)

Scapula

(shoulder blade)

Sternum

Humerus

Ribs

Fig 3.7 Bones of the neck, chest and shoulder girdle the top part of the sternum and at its lateral end it articulates with the scapula. The clavicle acts as a brace to hold the arm away from the top of the thorax.

The clavicle provides the only bony link between the shoulder girdle and the axial skeleton. The arrangement of bones and the muscle attached to the scapula and the clavicle allow for a considerable amount of movement of the shoulder and the upper limbs.

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