Ossicles

Ossicles refer to the three tiny bones of the middle ear that transmit mechanical energy and connect the tympanic membrane to the inner ear and cochlea. These three bones are known as the malleus (hammer), incus (anvil), and stapes (stirrup). These ossicles are the smallest bones in the human body.

Malleus

The malleus is the largest and most lateral ossicle among the three. It is composed of the handle, neck, and head processes. Rensink (2011) stated that the malleus has two landmarks – the long arm (manubrium) and the lateral process. The manubrium is classified as the body of the malleus. The end portion of the manubrium is shaped like a spatula. This also aids in the formation of the most depressed part and center of the eardrum, called the umbo. As seen in the picture below, the lateral process is a white ball that protrudes toward the ear canal.

Wageih Felfela (2017) said that the malleus is about 8 to 9 millimeters long and weighs about 25 milligrams. Its anterior process is the site of anterior malleolar ligament. It is also important to note that the malleus is 1.3 times longer than the incus. The anterior process is also near the manubrium and neck’s junction.

Attached below are images of the malleus.

Incus

The incus is also known as the anvil. This part provides the intermediate link between the ossicular chain. The malleus and incus articulate by means of saddle joint.

Wageih Felfela (2017) said that the incus is approximately 7 millimeters long and weighs 30 milligrams. The fossa incudis on the middle ear’s back wall accommodates the short process of the incus. Meanwhile, the long process of the incus descends to end at the lenticular process, a rounded nodule. This also articulates with the head of the stapes.

STAPES

The stapes is also known as the stirrup. This is the smallest and most medial bone of the ossicular chain. According to Wageih Felfela (2017), the stapes is roughly 3.5 millimeters long and the footplate surface area of 3.2 square millimeters weighs approximately 3 to 4 milligrams.

LIGAMENTS ATTACHED TO THE OSSICULAR CHAIN AND MIDDLE EAR WALLS

Wageih Felfela (2017) stated that various ligaments are attached to the ossicular chain. These are the superior malleal ligament, anterior malleal ligament, lateral malleal ligament, and posterior incudal ligament.

There are three ligaments attached to the malleus and one each for the stapes and incus.

The malleus’s anterior ligament is located above the anterior process. This is attached by one end to the neck of the malleus while the other end to the tympanic cavity’s anterior wall (close to the petrotympanic fissure). Some fibers are prolonged through the said fissure to reach the sphenoid’s spina angularis.

The malleus’s superior ligament descends from the roof of the epitympanic recess to the malleus’s head. This is characterized as a delicate, round bundle.

The malleus’s lateral ligament passes from the notch of Rivinius’s posterior part to the malleus’s head. The anterior and posterior portions of the lateral ligament forms the axis ligament, the malleus’s area of rotation. This lateral ligament is physically characterized as a triangular band.

The incus’s superior ligament looks a little more than a fold of the mucous membrane. Meanwhile, the posterior ligament of the incus connects the end of the short crus of the incus to the fossa incudis. This structure is described as a short, thick band.

The annular ligament of the base of the stapes is characterized as a fibrous ring. Moreover, hyaline cartilage covers the vestibular surface and the circumference of the base of the stapes. This area is attached to the fenestra vestibuli by the aforementioned annular ligament.

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