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Malleus


Type

irregular

Description

This is one of the three very small bones or ossicles in the middle ear cavity, its axes being about eight millimeters in length, it is the largest of the three ossicles. This small hammer-like bone forms a rounded, mallet-like head that projects from a slender handle. Near the junction of the head and handle are two small spine-like processes, the anterior and lateral processes. The handle or manubrium of the bone attaches to the tympanic membrane and relays the forces received there to the other ear ossicles. The bone has an interesting evolutionary history. It arises from the first or mandibular gill bar. In earlier vertebrates it was a posterior element, the articular bone, in the jaw apparatus. The mammals were the first vertebrates to incorporate this bone into the ear anatomy.

Etymology

Malleus is the Latin term for hammer or mallet. The early anatomists thought the bone resembled a hammer, therefore the name. The malleus and incus were discovered in 1503 by the anatomist, Alessandro Achillini. In 1543 Andreas Vesalius illustrated and named these bones in his writings.

Articulations

The malleus articulates with one other bone: the incus. The hammer-like head of the malleus forms a synovial articulation with the incus. This delicate articulation forms part of the mechanical linkage that amplifies the incoming sound waves in route to the fenestra vestibuli.

Ossification

The malleus ossifies in a cartilaginous anlage at the posterior end of the mandibular or Meckel's cartilage. A primary endochondral center appears during the fourth prenatal month in the cartilage. This center arises in the region of the neck. Soon after, a secondary center arises intramembranously. This center forms the anterior process and joins the primary center during the sixth fetal month. The bone is usually fully ossified by birth.

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