Of or pertaining to the thorax or chest: as, thoracic walls, contents, organs, or structures.Having a thorax (of this or that kind); belonging to the Thoracica: as, the thoracic cirripeds.Having the ventral fins thoracic in position; belonging to the Thoracici: as, a thoracic fish.Posterior thoracic, a branch from the upper two or three nerves of the brachial plexus, passing on the side of the chest to be distributed to the serratus magnus. Also called long thoracic, and external respiratory nerve of Bell.Especially, one of the several parts into which the surface of the human thorax is divided or mapped out by certain imaginary lines, which to some extent denote the situation of the contained viscera, and thus serve for medical and surgical purposes. These regions, unlike some of the corresponding abdominal regions, are all in pairs (right and left), in one nomenclature known as the humeral, subclavian, mammary, axillary, scapular, interscapular, and subscapular.n. A thoracic structure; especially, a thoracic artery or nerve, or a rib-bearing dorsal vertebra.n. A thoracic fish.