entosternal

These nine bones are in Geoffroy's nomenclature, the episternals, the hyosternals, the hyposternals, the xiphisternals, which are all paired bones, and the entosternal, which is unpaired.

Form and Function A Contribution to the History of Animal Morphology

The unpaired sternal bone (_urohyal_) cannot be homologous with the entosternal, for it has no connections with the annexes.

Form and Function A Contribution to the History of Animal Morphology

The minuteness of the episternals and the xiphisternals may be attributed to the gigantic size of the entosternal, in accordance with the _Loi de balancement_.

Form and Function A Contribution to the History of Animal Morphology

Thus in birds the sternum consists of five pieces, of a huge keeled entosternal, and of two "annexes" on either side, which are the hyo-and hyposternals.

Form and Function A Contribution to the History of Animal Morphology

As an example, take the minuteness of the episternals and xiphisternals in birds, as contrasted with the huge size of the entosternal.

Form and Function A Contribution to the History of Animal Morphology