Hyomandibulars

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The hyomandibula , also called epihyal , is a skeletal element of the second gill arch ( hyoid or hyoid arch ) of vertebrates . In original vertebrates it represents the upper part of the gill arch and in cranial animals it is integrated into the jaws of the bony skull . If there is bony , says Os hyomandibular or short hyomandibular .

The word component hyo or hy is short for Greek ὑοειδἡς hyoeides ( neo-Latin hyoides ) and means "υ-shaped". The word is derived from the Greek letter Ypsilon because the small Greek Ypsilon has this arched shape (υ). Hyomandibula therefore means something like "U-jaw" or "arched jawbone" (cf. mandible ).

Hyostyly

In most sharks and real bony fish, the hyomandibles provide an articulated connection between the jaws and the cranium in the area of ​​the ear capsules ( hyostyly ) in the form of the so-called jaw stem , which enables the entire jaw to move freely ; the jaw apparatus can be lowered and pushed back and forth independently. The associated first gill slit is narrowed by this suspension in the sharks to the spray hole (spiraculum). See also fish mouth .

Auditory ossicles of the terrestrial vertebrates

In the terrestrial vertebrates (Tetrapoda) the hyomandibular was transformed into an ossicle . In amphibians , reptiles and birds this represents the only small auditory ossicle as a small column ( Columella auris ). It forms an elongated bone rod and is with its base ( base columellae ) in the atrial window ( Fenestra vestibuli ; also oval window, Fenestra ovalis ), a small opening anchored between the middle and inner ear , which has formed as a depression of the contact point of the hyomandibulars on the ear capsule. It serves as a sound-transmitting part between the eardrum and the oval window.

In mammals , the hammer (malleus) and the anvil (incus) are two further auditory ossicles, which are formed from the upper and lower part of the first gill arch ( mandibular arch from mandibular and palatoquadratum ). The hyomandibular has a stirrup-like shape and is accordingly referred to as a stapes .

supporting documents

  1. ↑ a b Keyword “Hyomandibulare” In: Herder-Lexikon der Biologie. Spectrum Akademischer Verlag GmbH, Heidelberg 2003. ISBN 3-8274-0354-5 .
  2. ↑ a b c Wolfgang Maier, Lennart Olsen, Alfred Goldschmid: head. in: W. Westheide and R. Rieger: Special Zoology. Part 2. Vertebrate or skull animals. Spektrum, Munich 2004; P. 35. ISBN 3-8274-0307-3 .
  3. ↑ See Online Etymology Dictionary: hyoid (English)
  4. ↑ Hans-Peter Schultze: Gnathostomata, Kiefermünder. in: W. Westheide and R. Rieger: Special Zoology. Part 2. Vertebrate or skull animals. Spektrum, Munich 2004; 195. ISBN 3-8274-0307-3 .
  5. ^ Keyword “Columella” In: Herder-Lexikon der Biologie. Spectrum Akademischer Verlag GmbH, Heidelberg 2003. ISBN 3-8274-0354-5 .