The thoracic wall and diaphragm

The thoracic wall is made up of skeletal elements that form the thoracic cage (or more commonly, but less accurately, the rib cage) and muscles that move the components of the thoracic cage relative to each other for ventilation and postural movement. The thoracic cage is made up posteriorly by the thoracic part of the vertebral column, laterally and anteriorly by the ribs and costal cartilages, and by the sternum in the anterior mid-sternal area. The thoracic vertebral column is made up of 12 thoracic vertebrae and their intervertebral discs. The thoracic vertebrae are not arranged in a straight line, but are concave anteriorly as shown in Figure 9.2. All vertebrae have the following general configuration as shown in Figure 10.1A: • A heart-shaped body with two backward projections, the pedicles, either side of the vertebral foramen. The foramen forms the spinal canal with the foramina of other vertebrae. Note in Figure 10.1C that the pedicles are slightly shallow above and strongly grooved below to form intervertebral foramina with adjacent vertebrae for the passage of spinal nerves; • Two stout transverse processes running laterally and slightly posteriorly; • Two flat plates called laminae which join to form a long spinous process—you can feel the tips of the spinous processes very easily under the skin in the midline of your back; • Superior and inferior articular processes at the junction of the pedicles and laminae. In thoracic vertebrae, the superior facets are set vertically with the facets on the superior processes facing posterolaterally and those on the inferior processes anteromedially; the relative movement of the vertebrae is thus mainly rotary, but there is very little actual movement in the thoracic part of the vertebral column. The thoracic vertebrae are modified from this basic pattern to articulate with the ribs through several more articular facets as shown in Figure 10.1 A, B, and C. They carry on each side: • Shown most clearly in Figure 10.1 C, a superior and inferior demifacet (a half facet) on each side of the body for the heads of two ribs in the case of T2–T9 or a single complete facet for the head of one rib in the case of T1 and T10–T12; • Shown in Figure 10.1 A and B, a facet near the tip of each transverse process for the tubercle of a rib (except T11 and T12).