Rose Jacob A, Sandefur Mark, Huskey Steve, Demler Jennifer L, Butcher Michael T
Department of Biological Sciences, Youngstown State University, Youngstown, Ohio.
J Morphol. 2013 Nov;274(11):1277-87. doi: 10.1002/jmor.20178. Epub 2013 Aug 2.
Moles have modified thoracic limbs with hypertrophied pectoral girdle muscles that allow them to apply remarkably high lateral out-forces during the power stroke when burrowing. To further understand the high force capabilities of mole forelimbs, architectural properties of the thoracic limb muscles were quantified in the Eastern mole (Scalopus aquaticus). Architectural properties measured included muscle mass, moment arm, belly length, fascicle length, and pennation angle, and these were used to provide estimates of maximum isometric force, joint torque, and power. Measurements of muscle moment arms and limb lever lengths were additionally used to analyze the out-force contributions of the major pectoral girdle muscles. Most muscles have relatively long fascicles and little-to-no pennation. The humeral abductor/rotators as a functional group are massive and are capable of relatively high force, power, and joint torque. Of this group, the bipennate m. teres major is the most massive and has the capacity to produce the highest force and joint torque to abduct and axially rotate the humerus. In general, the distal limb muscles are relatively small, but have the capacity for high force and mechanical work by fascicle shortening. The muscle architectural properties of the elbow extensors (e.g., m. triceps brachii) and carpal flexors (e.g., m. palmaris longus) are consistent with the function of these muscles to augment lateral out-force application. The humeral abductor/rotators m. latissimus dorsi, m. teres major, m. pectoralis, and m. subscapularis are calculated to contribute 13.9 N to out-force during the power stroke, and this force is applied in a 'frontal' plane causing abduction of the humerus about the sternoclavicular joint. Moles have several specializations of their digging apparatus that greatly enhance the application of out-force, and these morphological features suggest convergence on limb form and burrowing function between New and Old World moles.
鼹鼠的胸肢经过了改造，其胸带肌肥大，这使它们在挖掘时的动力冲程中能够施加非常高的侧向向外力。为了进一步了解鼹鼠前肢的高力量能力，对东部鼹鼠（美洲鼹）胸肢肌肉的结构特性进行了量化。所测量的结构特性包括肌肉质量、力臂、肌腹长度、肌束长度和羽状角，这些用于估计最大等长力、关节扭矩和功率。此外，还测量了肌肉力臂和肢体杠杆长度，以分析主要胸带肌的向外力贡献。大多数肌肉的肌束相对较长，且几乎没有或没有羽状结构。作为一个功能组的肱骨外展/旋转肌体积庞大，能够产生相对较高的力量、功率和关节扭矩。在这个组中，双羽状的大圆肌是最大的，并且有能力产生最高的力量和关节扭矩来外展和轴向旋转肱骨。一般来说，肢体远端的肌肉相对较小，但通过肌束缩短有能力产生高力量和机械功。肘部伸肌（如肱三头肌）和腕部屈肌（如掌长肌）的肌肉结构特性与这些肌肉增强侧向向外力应用的功能一致。据计算，肱骨外展/旋转肌背阔肌、大圆肌、胸大肌和肩胛下肌在动力冲程中对外向力的贡献为13.9牛，并且这个力在一个“额状”平面上施加，导致肱骨围绕胸锁关节外展。鼹鼠的挖掘工具具有几个特殊之处，极大地增强了向外力的应用，这些形态特征表明新、旧大陆鼹鼠在肢体形态和挖掘功能上存在趋同现象。
