anatomical entity anatomical entity sternum http://upload.wikimedia.org/wikipedia/commons/1/12/Illu_thoracic_cage.jpg A midventral endochondral skeletal element which represents the origin site of the pectoral muscles[PHENOSCAPE:ad]. MA:0001331 AAO:0000765 relationship loss: part_of postzonal element (AAO:0000938)[AAO] uberon vertebrate sternum in birds, either ratite (no keel or carina) or carinate (keel and carina present) EHDAA:9561 GAID:246 in EMAPA and EHDAA2 this is part of the skeleton of pectoral girdle; the classic def of pectoral girdle (see WP) excludes the rib cage and sternum breastbone MESH:D013249 Fishes lack a sternum. (...) A sternum is absent in the first fossil tetrapods, but it is present in modern amphibians. (...) Thus, a sternum occurs in some modern amphibians, birds, mammals and archosaurs. However, its absence in the common ancestors to these groups means that it has arisen independently several times within the field of the midventral connective tissue.[well established][VHOG] galen:Sternum BTO:0001302 Single element that constitutes the postzonal area of the pectoral girdle.[AAO] UMLS:C0038293 OpenCyc:Mx4rvVjO6JwpEbGdrcN5Y29ycA CALOHA:TS-0972 EMAPA:18344 UBERON:0000975 It probably first evolved in early tetrapods as an extension of the pectoral girdle; it is not found in fish. In amphibians and reptiles it is typically a shield-shaped structure, often composed entirely of cartilage. It is absent in both turtles and snakes. In birds it is a relatively large bone and typically bears an enormous projecting keel to which the flight muscles are attached. Only in mammals does the sternum take on the elongated, segmented form seen in humans. In some mammals, such as opossums, the individual segments never fuse and remain separated by cartilagenous plates throughout life FMA:7485 VHOG:0000856 NCIT:C12793 While its developmental origins are similar to the ribs (from the myospetum and septum of the trunk region), it is often associated with the pectoral skeleton, due to both function and physical connections (i.e. the coracoid of archosaurs). It may be a single element or a series of smaller structure (sternebrae). Based on Kardong 2012. [PHENOSCAPE:ad]. sternal EHDAA2:0001914 thoracic segment organ endochondral element