Stern J T, Wells J P, Jungers W L, Vangor A K, Fleagle J G
Am J Phys Anthropol. 1980 Jan;52(1):13-25. doi: 10.1002/ajpa.1330520104.
Among primates there is striking variation in the extent of the origin of pectoralis major from the clavicle. A significant clavicular attachment (pars clavicularis) occurs only in Alouatta, Lagothrix, Hylobates, Pan (troglodytes, paniscus and gorilla), and Homo. Interpreting this trait in nonhuman primates as an adaptation to frequent use of a mobile forelimb in climbing and suspension is contraindicated by the absence of a clavicular origin in Ateles and Pongo. We have undertaken a telemetered electromyographic study to determine any special role of the most cranial part of the pectoralis major in comparison to its caudal part, and to the deltoid, during vertical climbing, pronograde quadrupedalism, and armswinging in Ateles, Lagothrix, Alouatta, and Hylobates. The results show that the cranial pectoralis major possesses a role not shared by the caudal fibers: initiation of the recovery phase of the locomotor cycle. When ability to execute rapid or powerful recovery of the adducted forelimb is required in an animal with a shoulder joint lying on a plane cranial to that of the manubrium, the movement will be facilitated if the origin of the pectoralis major is extended onto the clavicle. Such is the case in nonhuman primates possessing this trait. The absence of a clavicular origin in Ateles and Pongo may be related to diminished selective pressures to perfect locomotor modes such as pronograde quadrupedalism, armswinging, or climbing thick vertical trunks, that demand rapid or powerful recovery of the adducted forelimb. If the arboreal ancestor of humans had evolved a clavicular origin of pectoralis major, this animal would be preadapted for certain uses of the forelimb in its bipedal descendant.
在灵长类动物中，胸大肌起于锁骨的范围存在显著差异。明显的锁骨附着部分（锁骨部）仅见于蛛猴属、绒毛猴属、长臂猿属、黑猩猩属（黑猩猩、倭黑猩猩和大猩猩）以及人类。蜘蛛猴属和猩猩属没有锁骨起始部，这表明将非人类灵长类动物的这一特征解释为对攀爬和悬吊中频繁使用灵活前肢的适应是不合适的。我们进行了一项遥测肌电图研究，以确定在蜘蛛猴属、绒毛猴属、蛛猴属和长臂猿属动物垂直攀爬、前位四足行走和摆臂运动过程中，胸大肌最靠上部分相对于其靠下部分以及三角肌而言是否具有特殊作用。结果表明，胸大肌靠上部分具有靠下肌纤维所不具备的作用：启动运动周期的恢复阶段。对于肩关节位于胸骨柄平面上方的动物而言，当需要快速有力地恢复内收前肢的能力时，如果胸大肌的起始部延伸至锁骨，那么这一动作将更易完成。具有这一特征的非人类灵长类动物就是如此。蜘蛛猴属和猩猩属没有锁骨起始部，可能与完善诸如前位四足行走、摆臂或攀爬粗壮垂直树干等运动模式的选择压力减小有关，而这些运动模式需要快速有力地恢复内收前肢。如果人类的树栖祖先进化出了胸大肌的锁骨起始部，那么这种动物就会为其双足后代前肢的某些用途做好预先适应。
