Cheung Bob, Ercoline William
Aerosp Med Hum Perform. 2018 Aug 1;89(8):744-748. doi: 10.3357/AMHP.5104.2018.
Orientation in a 3-dimensional environment increases demands on the vestibular system. The anterior, lateral, and posterior semicircular canals sense pitch, roll, and yaw acceleration, respectively. The macular end organs sense linear acceleration and provide gravity reference. Creatures that evolved to fly (birds) share the same sensory systems and probably the same limitations as creatures that did not evolve to fly. However, bird semicircular canals have been noted for their large size relative to body mass since 1907.
A brief literature review was conducted regarding the morphological structure of the vestibular systems in birds, and their evolutionary and functional significance as compared to that in humans.
For any given body mass, qualitatively more "agile" species have semicircular canals with larger radius of curvature. Specifically, the anterior and lateral canals were found to be preferentially larger than those of nonavian theropods and humans. Avian canals rarely approach circularity and all three canals typically undergo torsional excursions out of their respective planes.
Increase in the length of the semicircular canal is associated with greater sensitivity to rotational stimuli. Highly maneuverable birds of prey have the largest overall canal dimensions relative to body mass, most plausibly to match the rapid body rotations that characterize variable speed maneuvering during pursuit. By comparison, the semicircular canals in humans are relatively smaller and lack the adaptive morphological asymmetry in agile flying species. This teleological symmetry may present another inherent but less understood vestibular limitation during aerobatic maneuvers, which could lead to spatial disorientation.Cheung B, Ercoline W. Semicircular canal size and shape influence on disorientation. Aerosp Med Hum Perform. 2018; 89(8):744-748.
在三维环境中定向会增加对前庭系统的需求。前、外和后半规管分别感知俯仰、横滚和偏航加速度。黄斑终器感知线性加速度并提供重力参考。进化为能飞行的生物（鸟类）与未进化为能飞行的生物拥有相同的感觉系统，可能也存在相同的局限性。然而，自1907年以来，鸟类的半规管就因其相对于体重的较大尺寸而受到关注。
对鸟类前庭系统的形态结构及其与人类相比的进化和功能意义进行了简要的文献综述。
对于任何给定的体重，定性地说，更“敏捷”的物种具有半径更大的半规管。具体而言，发现鸟类的前半规管和外侧半规管比非鸟类兽脚亚目恐龙和人类的更大。鸟类半规管很少接近圆形，并且所有三个半规管通常都会偏离各自的平面进行扭转偏移。
半规管长度的增加与对旋转刺激的更高敏感性相关。相对于体重而言，机动性强的猛禽具有最大的总体半规管尺寸，最有可能是为了匹配追捕过程中变速机动所特有的快速身体旋转。相比之下，人类的半规管相对较小，并且缺乏敏捷飞行物种中存在的适应性形态不对称。这种目的论上的对称性可能在特技飞行机动过程中带来另一种内在但鲜为人知的前庭局限性，这可能导致空间定向障碍。
张B，埃尔科林W。半规管大小和形状对定向障碍的影响。航空航天医学与人类表现。2018；89(8):744 - 748。
