Satoh K
Department of Zoology, Faculty of Science, Kyoto University, Japan.
J Morphol. 1998 Apr;236(1):49-56. doi: 10.1002/(SICI)1097-4687(199804)236:1<49::AID-JMOR3>3.0.CO;2-J.
The functional significance of masticatory muscle direction was estimated using a mechanical model in two murid rodents: the Japanese field mouse (Apodemus speciosus) and the gray red-backed vole (Clethrionomys rufocanus). Theoretical analyses of the data suggest that a balancing mechanism among the muscle forces occurs during incisal power stroke. The activation of the large deep masseter in both murids results in marked tensile separation of two hemimandibles at the flexible mandibular symphysis. Activation of the internal pterygoid decreases this large tensile force at the symphysis more efficiently than other muscles. The lines of action of the deep masseter and internal pterygoid are aligned to produce such a balancing function in both species studied here. The resultant force generated by the deep masseter on both sides is opposite in direction to the reaction force at the lower incisor tip. Therefore, the large deep masseter forms an effective mandibular support mechanism when the reaction forces during biting push the mandible downward. Because of the area of insertion and the line of action, the posterior temporalis appears to have an important role in stabilizing the position of the mandibular condyle in the glenoid fossa during incisal biting.
利用力学模型对两种鼠科啮齿动物——日本田鼠（Apodemus speciosus）和棕背䶄（Clethrionomys rufocanus）咀嚼肌方向的功能意义进行了评估。对数据的理论分析表明，在切牙动力冲程期间，肌肉力量之间存在一种平衡机制。两种鼠科动物中大型深层咬肌的激活都会导致两半下颌骨在灵活的下颌联合处明显拉伸分离。翼内肌的激活比其他肌肉更有效地降低了联合处的这种大拉力。深层咬肌和翼内肌的作用线对齐，在此处研究的两个物种中产生这种平衡功能。两侧深层咬肌产生的合力方向与下切牙尖端的反作用力相反。因此，当咬合时的反作用力将下颌向下推时，大型深层咬肌形成了一种有效的下颌支撑机制。由于插入面积和作用线的原因，颞肌后部似乎在切牙咬合时稳定下颌髁突在关节窝中的位置方面发挥着重要作用。
