The sternum in UNGULATA is generally long and narrow and formed of six or generally seven segments. The presternum is as a rule small and compressed, often much keeled, especially in the horse and tapir. The segments of the mesosternum gradually widen as followed back and the xiphisternum is often terminated by a cartilaginous plate. In the RODENTIA the sternum is long and narrow and generally has a large presternum, and a xiphisternum terminated by a broad cartilaginous plate. In the CARNIVORA, too, the sternum (fig. 76) is long and narrow and formed of eight or nine pieces, all of nearly the same size. The xiphisternum generally ends in an expanded plate of cartilage. In INSECTIVORA the sternum is well developed but variable. The presternum is commonly large and is sometimes as in the Hedgehog (_Erinaceus_) bilobed in front, sometimes as in the Shrew (_Sorex_) trilobed. It is especially large in the Mole (_Talpa_) and is expanded laterally and keeled below. In the CHIROPTERA the presternum is strongly keeled and so is sometimes the mesosternum. Among PRIMATES, in Man and the Anthropoid Apes the sternum is rather broad and flattened; the mesosternum consists of four segments which are commonly fused together and the xiphisternum is imperfectly ossified. THE RIBS. Free ribs are borne as a rule only by the thoracic vertebrae; ribs may be found in other regions, especially the cervical and sacral, but these are almost always ankylosed to the vertebrae. As a general rule the first thoracic rib joins the presternum, while the succeeding ones are attached between the several segments of the mesosternum. Some of the posterior ribs frequently do not reach the sternum; they may then be attached by fibrous tissue to the ribs in front, or may end freely (_floating ribs_). There are generally thirteen pairs of ribs, and in no case do they have uncinate processes. In MONOTREMES (fig. 102, B) each rib is divided not into two but into three parts, an intermediate portion being interposed between the vertebral and sternal parts. The sternal ribs are well ossified, and some are very broad and flat. The intermediate portions are unossified, those of the anterior ribs are short and narrow, but they become longer and wider further back. In MARSUPIALS there are almost always thirteen pairs of ribs, whose sternal portions are very imperfectly ossified. _Notoryctes_ has fourteen pairs of ribs, eight of which are floating: the first rib is very stout, and is abruptly bent on itself to join the sternum. It has no distinct sternal portion. All the other ribs are slender. Of the EDENTATES the Sloths have very numerous ribs; twenty-four pairs occur in _Choloepus_, and half of these reach the sternum. In the Armadillos there are only ten or twelve pairs of ribs, but the sternal portions are very strongly ossified. The first rib is remarkably broad and flat, and is not divisible into vertebral and sternal portions.