Angular bone

<p>The angular is a large <a href="/facts/Bone/kwJaR6IQ">bone</a> in the <a href="/facts/Lower_jaw/1ATEfAQa">lower jaw</a> (mandible) of <a href="/facts/Amphibians/r2BleD2W">amphibians</a> and <a href="/facts/Reptiles/04n1uKf1">reptiles</a> (<a href="/facts/Birds/RJF6zwLP">birds</a> included), which is connected to all other lower jaw bones: the <a href="/facts/Dentary/1ATEfAQa">dentary</a> (which is the entire lower jaw in <a href="/facts/Mammals/phSwTzBo">mammals</a>), the <a href="/facts/Splenial/lvGWREV1">splenial</a>, the <a href="/facts/Suprangular/Btcv81Wv">suprangular</a>, and the <a href="/facts/Articular/mtMzom1h">articular</a>. It is <a href="/facts/Homology_(biology)/muctKlyT">homologous</a> to the <a href="/facts/Tympanic_bone/BfQE8enj">tympanic bone</a> in mammals, due to the <a href="/facts/Evolution_of_mammalian_auditory_ossicles/QaIQKcRu">incorporation of several jaw bones into the mammalian middle ear</a> early in mammal evolution.
</p><p>In <a href="/facts/Therapsida/P4ERDjA2">therapsids</a> (mammal ancestors and their kin), the lower jaw is made up of the <a href="/facts/Dentary/1ATEfAQa">dentary</a> (the <a href="/facts/Mandible/1ATEfAQa">mandible</a> in mammals) and a group of smaller "postdentary" bones near the jaw joint. As the dentary increased in size over millions of years, two of these postdentary bones, the articular and angular, became increasingly reduced and the dentary eventually made direct contact with the upper jaw. These postdentary bones, even before their articular function was lost, probably transmitted sound vibrations to the stapes and, in some therapsids, a bent plate that might have supported a membrane capable of detecting vibrations developed on the angular. Eventually, it developed into the <a href="/facts/Ectotympanic/eHqvTu8b">ectotympanic</a> ring which supports the <a href="/facts/Tympanic_membrane/2mHLYSMF">tympanic membrane</a> in the ears of modern mammals.
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Angular bone open-in-new

Angular bone