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Chapter 4
The thorax
THE THORACIC CAGE CHAPTER CONTENTS The thoracic cage 107 The diaphragm 111 The pleura 114 The trachea and bronchi 116 The lungs 118 The mediastinal divisions 124 The heart 125 The great vessels 133 The oesophagus 136 The thoracic duct and mediastinal lymphatics 139 The thymus 139 The azygos system 140 Important nerves of the mediastinum 142 The mediastinum on the chest radiograph 143 Cross-sectional anatomy 145
The roof of the thoracic cage is formed by the suprapleural membrane and the diaphragm is its floor. The walls are made of the skeleton and attached muscles. The bones involved are: (i) 12 thoracic vertebrae (see section on vertebral column); (ii) 12 ribs and their costal cartilages and (iii) the sternum. The ribs There are 12 pairs of ribs - 7 true, 3 false and 2 floating. Occasionally a normal subject has only 11 pairs. The typical rib (Fig. 4. 1) A typical rib has a head, neck, tubercle and shaft. The head has two facets for articulation with vertebral bodies, for example the sixth rib articulates with the bodies of T5 and T6 vertebrae. These costovertebral joints are synovial joints. The neck of the rib is attached by a ligament to the transverse process of the vertebra above. The tubercle has a facet medially for articulation with its own transverse process. This costotransverse joint is also a synovial joint. The tubercle also has a nonarticular part laterally for ligament attachment.
