What is the X in X-mas?
"chest," c.1400, from Latin thorax, from Greek thorax (genitive thorakos) "breastplate, chest," of unknown origin.
thorax tho·rax (thôr'āks')
n. pl. tho·rax·es or tho·ra·ces (thôr'ə-sēz')
The part of the human body between the neck and the diaphragm, partially encased by the ribs and containing the heart and lungs; the chest.
A part in other vertebrates that corresponds to the human thorax.
The second or middle region of the body of an arthropod, between the head and the abdomen, in insects bearing the legs and wings.
Plural thoraxes or thoraces (thôr'ə-sēz')
The part of the body between the neck and diaphragm; the chest.
in amphibians, reptiles, birds, and mammals, the chest. In humans and other mammals the chest is that part of the body between the neck and abdomen. In humans the bony framework of the thorax consists of the 12 thoracic vertebrae, 12 pairs of ribs, and the sternum (breastbone). The mammalian thorax contains the chief organs of respiration and circulation, namely, the lungs, some air passages, the heart, and the great vessels (see thoracic cavity). Below, it is bounded by the diaphragm. The bony framework is encased with muscles, fat, and cutaneous tissues.