My Science School

The stapes is the smallest and lightest bone in the human body at 3mm x 2.5 mm in size. The shape of a stirrup, it is one of three tiny bones in the middle ear, collectively known as the ossicles, that convey sound waves from the outer ear to the inner ear. The other two are the malleus (hammer) and the incus (anvil).

The stapes develops from the second pharyngeal arch during the sixth to eighth week of embryological life. The central cavity of the stapes, the obturator foramen, is due to the presence embryologically of the stapedial artery, which usually regresses in humans during normal development.

The stapes is one of three ossicles in mammals. In non-mammalian four-legged animals, the bone homologous to the stapes is usually called the columella; however, in reptiles, either term may be used. In fish, the homologous bone is called the hyomandibular, and is part of the gill arch supporting either the spiracle or the jaw, depending on the species. The equivalent term in amphibians is the pars media plectra.

The stapes appears to be relatively constant in size in different ethnic groups. In 0.01–0.02% of people, the stapedial artery does not regress, and persists in the central foramen. In this case, a pulsatile sound may be heard in the affected ear, or there may be no symptoms at all. Rarely, the stapes may be completely absent.

Picture Credit : Google