Iriarte-Diaz Jose, Terhune Claire E, Taylor Andrea B, Ross Callum F
Department of Oral Biology, University of Illinois at Chicago, 801 S. Paulina St., Chicago, IL 60612, USA.
Department of Anthropology, University of Arkansas, Fayetteville, AR 72701, USA.
Zoology (Jena). 2017 Oct;124:106-118. doi: 10.1016/j.zool.2017.08.006. Epub 2017 Aug 23.
The location of the axis of rotation (AoR) of the mandible was quantified using the helical axis (HA) in eight individuals from three species of non-human primates: Papio anubis, Cebus apella, and Macaca mulatta. These data were used to test three hypotheses regarding the functional significance of anteroposterior condylar translation - an AoR located inferior to the temporomandibular joint (TMJ) - during chewing: minimizing impingement of the gonial region on cervical soft tissue structures during jaw opening; avoiding stretching of the inferior alveolar neurovascular bundle (IANB); and increasing jaw-elevator muscle torques. The results reveal that the HA is located near the occlusal plane in Papio and Cebus, but closer to the condyle in Macaca; is located anteroinferior to the TMJ during both opening and closing in Papio, as well as during opening in Macaca and Cebus; and varies in its location during closing in Macaca and Cebus. The impingement hypothesis is not supported by interspecific variation in HA location: species with larger gonial angles like Cebus do not have more inferiorly located HAs than species with more obtuse mandibular angles like Papio. However, intraspecific variation provides some support for the impingement hypothesis. The HA seldom passes near or through the lingula, falsifying the hypothesis that its location is determined by the sphenomandibular ligament, and the magnitudes of strain associated with a HA at the TMJ would not be large enough to cause problematic stretching of the IANB. HA location does affect muscle moment arms about the TMJ, with implications for the torque generation capability of the jaw-elevator muscles. In Cebus, a HA farther away from the TMJ is associated with larger jaw-elevator muscle moment arms about the joint than if it were at the TMJ. The effects of HA location on muscle strain and muscle moment arms are largest at large gapes and smallest at low gapes, suggesting that if HA location is of functional significance for primate feeding system performance, it is more likely to be in relation to large gape feeding behaviors than chewing. Its presence in humans is most parsimoniously interpreted as a primitive retention from non-human primate ancestors and explanations for the presence of anteroposterior condylar translation in humans need not invoke either the uniqueness of human speech or upright posture.
利用螺旋轴（HA）对三种非人灵长类动物（东非狒狒、卷尾猴和猕猴）的8只个体的下颌骨旋转轴（AoR）位置进行了量化。这些数据用于检验关于髁突前后平移（即位于颞下颌关节（TMJ）下方的AoR）在咀嚼过程中的功能意义的三个假设：在张口时使下颌角区域对颈部软组织结构的撞击最小化；避免下牙槽神经血管束（IANB）拉伸；以及增加升颌肌扭矩。结果显示，HA在狒狒和卷尾猴中位于咬合平面附近，但在猕猴中更靠近髁突；在狒狒张口和闭口时以及猕猴和卷尾猴张口时，HA位于TMJ的前下方；在猕猴和卷尾猴闭口时，HA的位置有所不同。HA位置的种间差异不支持撞击假设：像卷尾猴这样下颌角较大的物种，其HA位置并不比像狒狒这样下颌角更钝的物种更低。然而，种内差异为撞击假设提供了一些支持。HA很少靠近或穿过翼突小钩，这使得其位置由蝶下颌韧带决定这一假设不成立，并且与TMJ处HA相关的应变大小不足以导致IANB出现有问题的拉伸。HA位置确实会影响围绕TMJ的肌肉力臂，这对升颌肌的扭矩产生能力有影响。在卷尾猴中，远离TMJ的HA与围绕关节的更大升颌肌力臂相关，而如果HA位于TMJ处则不然。HA位置对肌肉应变和肌肉力臂的影响在大张口时最大，在小张口时最小，这表明如果HA位置对灵长类动物进食系统性能具有功能意义，那么它更可能与大张口进食行为而非咀嚼有关。它在人类中的存在最简洁的解释是从非人类灵长类祖先那里保留下来的原始特征，并且对于人类髁突前后平移的存在的解释无需援引人类语言或直立姿势的独特性。
