Department of Anatomical Sciences, Stony Brook University School of Medicine, Stony Brook, NY 11794-8081, USA.
J Hum Evol. 2013 Oct;65(4):391-403. doi: 10.1016/j.jhevol.2013.07.010. Epub 2013 Aug 19.
It is widely held that many differences among primate species in scapular morphology can be functionally related to differing demands on the shoulder associated with particular locomotor habits. This perspective is largely based on broad scale studies, while more narrow comparisons of scapular form often fail to follow predictions based on inferred differences in shoulder function. For example, the ratio of supraspinous fossa/infraspinous fossa size in apes is commonly viewed as an indicator of the importance of overhead use of the forelimb, yet paradoxically, the African apes, the most terrestrial of the great apes, have higher scapular fossa ratios than the more suspensory orangutan. The recent discovery of several nearly complete early hominin scapular specimens, and their apparent morphological affinities to scapulae of orangutans and gorillas rather than chimpanzees, has led to renewed interest in the comparative analysis of human and extant ape scapular form. To facilitate the functional interpretation of differences in ape scapulae, particularly in regard to relative scapular fossa size, we used electromyography (EMG) to document the activity patterns in all four rotator cuff muscles in orangutans and gibbons, comparing the results with previously published data for chimpanzees. The EMG results indicate that the distinctive contributions of each cuff muscle to locomotion are the same in the three ape species, failing to support inferences of differences in rotator cuff function based on relative scapular fossa size comparisons. It is also shown that relative scapular fossa size is not in fact a good predictor of either the relative masses or cross-sectional areas of the rotator cuff muscles in apes, and relative fossa size gives a false impression of the importance of individual cuff muscles to locomotor differences among apes. A possible explanation for the disparity between fossa and muscle size relates to the underappreciated role of the scapular spine in structural reinforcement of the blade.
人们普遍认为，灵长类动物的肩胛骨形态存在许多差异，这些差异与特定的运动习惯相关的肩部需求有关。这种观点主要基于广泛的研究，而对肩胛骨形态的更窄范围的比较往往无法遵循基于推断的肩部功能差异的预测。例如，在猿类中，肩峰下窝/肩峰下窝大小的比例通常被视为前肢使用头顶的重要性的指标，但矛盾的是，非洲猿类是最像地栖的大型猿类，其肩胛骨窝的比例高于更具悬挂性的猩猩。最近发现了几个几乎完整的早期人类肩胛骨标本，它们与猩猩和大猩猩的肩胛骨形态明显相似，而不是与黑猩猩相似，这导致人们重新关注人类和现生灵长类动物肩胛骨形态的比较分析。为了便于解释猿类肩胛骨差异的功能，特别是在相对肩胛骨窝大小方面，我们使用肌电图（EMG）记录了猩猩和长臂猿所有四个肩袖肌肉的活动模式，并将结果与之前发表的黑猩猩数据进行了比较。EMG 结果表明，在这三个猿类物种中，每个肩袖肌肉对运动的独特贡献是相同的，这与基于相对肩胛骨窝大小比较的肩袖功能差异推断不符。还表明，相对肩胛骨窝大小实际上并不是预测猿类肩袖肌肉相对质量或横截面积的良好指标，并且相对窝大小给人一种假象，即单个肩袖肌肉对猿类运动差异的重要性。窝和肌肉大小之间的差异可能与肩胛骨脊柱在叶片结构加固中的作用被低估有关。
