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The ossicles (also called auditory ossicles) are three irregular bones in the middle ear of humans and other mammals, and are among the smallest bones in the human body. . Although the term "ossicle" literally means "tiny bone" (from Latin ossiculum) and may refer to any small bone throughout the body, it typically refers specifically to the malleus, incus and stapes ("hammer, anvil, and ...
The ossicles may bear external projections in the form of spines, granules or warts and they are supported by a tough epidermis. Skeletal elements are sometimes deployed in specialized ways, such as the chewing organ called "Aristotle's lantern" in sea urchins, the supportive stalks of crinoids, and the structural "lime ring" of sea cucumbers. [13]
They form part of the endoskeleton and provide rigidity and protection. They are found in different forms and arrangements in sea urchins, starfish, brittle stars, sea cucumbers, and crinoids. The ossicles and spines (which are specialised sharp ossicles) are the only parts of the animal likely to be fossilized after an echinoderm dies.
The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear).. The mammalian middle ear contains three ossicles (malleus, incus, and stapes), which transfer the vibrations of the eardrum into waves in the fluid and membranes of the inner ear.
The ossicles from which the stem is composed are known as columnals. They are discs with a circular, pentagonal, star-shaped or elliptical cross section. The stem is flexible and the columnals are connected to each other with ligaments. At each node where the columnals articulate with each other there may be a whorl of five cirri. These ...
The auditory ossicles continue to function in conducting transmitting sound through the auditory pathway; however, they have lost their function in conducting low frequency ground vibrations. Later-arising reptiles with columella likely evolved stronger limbs and a more crawling posture, which removed the body from the ground and prevented the ...
The stapes is one of three ossicles in mammals. In non-mammalian tetrapods , 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 evolution of mammalian auditory ossicles was an evolutionary process that resulted in the formation of the mammalian middle ear, where the three middle ear bones or ossicles, namely the incus, malleus and stapes (a.k.a. "the anvil, hammer, and stirrup"), are a defining characteristic of mammals.