the bony structure enclosing the thorax, consisting of the ribs, vertebral column and sternum. thoracic cavity. see thorax; called also chest. thoracic duct ligation. a surgical procedure used in the treatment of chylothorax where medical management is unsuccessful.thoracic girdle. the incomplete ring of bones that support the thoracic limb, made up of the scapula, clavicle, coracoid and occasionally other elements.horacic wall. includes the ribs, sternum and thoracic vertebrae, the intercostal, superficial and deep, muscles, and the external respiratory muscles (transverse thoracic, rectus thoracic, serratus dorsalis and scalenus), and the costal pleura.