Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Musculoskeletal System
Bones of the Trunk and Their Joints
Thorax

The BONES OF THE thorax are formed by 12 pairs of Ribs, the Sternum, and the thoracic vertebrae.

The ribs are long, curved bony plates that transition into costal cartilages anteriorly. Posteriorly, each rib terminates in a thickened HEAD that articulates with the bodies of the corresponding vertebrae. Slightly anterior to the head lies the tubercle of the rib, which forms a joint with the transverse process of the vertebra. Along the lower border on the inner side of each rib runs a groove housing the intercostal artery, vein, and nerve. The upper seven pairs of ribs (I—VII) attach directly to the sternum at their anterior ends and are referred to as true ribs. Ribs VIII—X do not reach the sternum; instead, they attach to the Cartilage of the ribs immediately above them and are therefore known as false ribs. Ribs XI and XII terminate in the Muscles of the anterior abdominal wall, leaving their anterior ends free. These ribs are highly mobile and are termed floating ribs.

The sternum is a flat bone comprising the manubrium, body, and xiphiod process. Its lateral borders feature notches for articulation with the costal cartilages.

The sternum, 12 pairs of ribs, and 12 thoracic vertebrae interconnect via joints, cartilaginous junctions, and ligaments to form The thoracic cage. The thoracic cage presents four walls—anterior, posterior, and two lateral—which enclose the thoracic cavity. The thoracic cavity contains Internal Organs (The Heart, Lungs, Trachea, and Esophagus), as well as major Blood Vessels and nerves. Intercostal spaces located between adjacent ribs are filled with intercostal muscles.

The thorax features two apertures: superior and inferior. The superior thoracic aperture is bounded laterally by the first ribs, anteriorly by the upper border of the manubrium of the sternum, and posteriorly by the body of the first thoracic vertebra. Structures passing through the superior aperture include the trachea, esophagus, Blood Vessels, and nerves. The inferior thoracic aperture is bounded by the lower ribs, anteriorly by the xiphoid process, and posteriorly by the body of the twelfth thoracic vertebra. Inferior to the xiphoid process lies the infrasternal angle (its apex). The lateral walls of this angle are formed by the right and left costal margins, created by the joined cartilaginous ends of ribs VII—X. The inferior aperture of the thorax is significantly larger than the superior one. The Muscle closing the inferior aperture—the Diaphragm (thoracoabdominal partition)—features openings for the passage of the aorta, esophagus, nerves, and INFERIOR VENA CAVA.

Depending on body build, three shapes of the thorax are distinguished. In short, stocky individuals (brachymorphic body type), the thorax is short, broad, and conical in shape, with an obtuse infrasternal angle. In tall individuals (dolichomorphic body type), it is elongated and flat, with an acute infrasternal angle. In individuals of average height (mesomorphic body type), the thorax is cylindrical. In women, the thorax is shorter and narrower inferiorly than in men.

The thorax can become deformed due to improper posture and certain pathological conditions. For instance, if a schoolchild slumps over the desk while writing, the thorax may develop a flattened or asymmetrical shape.

The thoracic cage possesses notable strength and mobility. During Respiration, it changes both in volume and shape. Upon inspiration, the sternum and the anterior ends of the ribs elevate, increasing the anteroposterior diameter of the thorax while widening the intercostal spaces. Upon expiration, the sternum and the anterior ends of the ribs depress, reducing the anteroposterior diameter and overall volume of the thorax.