Thoracic vertebrae composed the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae.
In 2152, Gosis noted that Jonathan Archer and Malcolm Reed were missing four thoracic vertebrae, compared to his own species. (ENT: "The Communicator")
In 2369, a clone of Ibudan was killed when a knife was thrust directly between his left and right thoracic vertebrae, perforating the lower ventricle of his heart. (DS9: "A Man Alone")
Later that year, Julian Bashir reported that Kai Opaka's upper thoracic vertebrae were crushed following the crash of the USS Yangtzee Kiang. (DS9: "Battle Lines")