Rib Cage and Thoracic Spine Explorer

A grouping by what the rib reaches at the front, not by the bone itself. The first seven pairs join the sternum through their own costal cartilage and are called true ribs. The eighth, ninth and tenth join the cartilage above them rather than the sternum directly, which makes them false ribs. The eleventh and twelfth end in the muscle of the abdominal wall and reach nothing at the front at all, which is why they are called floating. This model carries the bone, so the distinction shows up as which ribs curve round towards the sternum and which stop short: turn to the front view and follow the eleventh and twelfth forward to see them end.

Because its three parts ossify separately, and the dataset segments them apart. The xiphoid usually fuses to the body by middle age, but the manubrium usually stays joined to the body by cartilage for life. The manubrium is the broad top piece that meets the clavicles, the body is the long middle, and the xiphoid process is the small tip, which is cartilage in youth and often does not fully ossify until middle age. Measured on this specimen the manubrium sits about 140 millimetres above the xiphoid, so the sternum is a good deal longer than most diagrams suggest. The joint between the manubrium and the body is a real landmark: it sits level with the second rib, which is how you count ribs on a patient.

Because of their shape. The 24 ribs are 755,704 triangles between them, averaging about 31,500 each, and that total is three times the whole skull. A rib is a long thin curved shell, and that is the worst case for a triangle budget: a surface that encloses almost no volume has nothing to amortise its own area against, where a compact bone like a vertebra gets a lot of shape for comparatively few triangles. That makes this the heaviest skeletal region on the site after the full skeleton, and the size is printed on the load button so you can decide before it downloads.

Yes, all sixteen costal cartilage meshes the dataset publishes, in their own pale band. This was the first skeletal region here to carry anything other than bone, and the full skeleton now does the same with its intervertebral discs and membranes. They were left out of the first version on the principle that the site shows bone, and the result looked broken rather than incomplete: every rib ended in mid air a long way from the sternum and the front of the cage read as a rendering fault. The dataset publishes the first to seventh individually on each side plus one further mesh per side that it simply calls the costal cartilage, and all of them are here. Hide the band to see what the bone alone looks like.