Ito Kai, Endo Hideki
Graduate School of Agricultural and Life Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku Tokyo 113-0033, Japan.
J Vet Med Sci. 2019 Mar 14;81(3):389-396. doi: 10.1292/jvms.18-0611. Epub 2019 Jan 22.
We compared the temporomandibular joint structure between species of the order Carnivora and investigated its variation among family lineages. We also investigated the effect of the masticatory muscle physiological cross-sectional area (PCSA) on temporomandibular joint structure. The masticatory muscle is composed of multiple muscles, which contract in different directions and exert pressure on the temporomandibular joint. We investigated the effect of the ratio of each muscle's PCSA-an indicator of muscle force-and muscle size relative to body size on temporomandibular joint structure. The temporalis PCSA relative to body size showed the highest correlation with temporomandibular joint structure. When the temporalis PCSA is large relative to body size, the preglenoid projects caudally, the postglenoid projects rostrally and the pre-postglenoid angle interval is small, indicating that the condyle is locked in the fossa to reinforce the temporomandibular joint. Most Carnivora use blade-like carnassial teeth when slicing food. However, dislocation occurs when the carnassial teeth are used by the temporalis muscle. Our results suggest that the temporomandibular joint is reinforced to prevent dislocation caused by the temporalis muscle. In Mustelidae, the temporomandibular joint with a rostrally projecting postglenoid is suitable for carnassial biting using the temporalis muscle. In Felidae, the force of the masseter onto the carnassial teeth is diverted to the canine by tightening the temporomandibular joint. In Canidae, the masticatory muscle arrangement is well-balanced, enabling combined action. Hence, reinforcement of the temporomandibular joint by bone structure is unnecessary.
我们比较了食肉目物种之间的颞下颌关节结构，并研究了其在科系中的变化。我们还研究了咀嚼肌生理横截面积（PCSA）对颞下颌关节结构的影响。咀嚼肌由多块肌肉组成，这些肌肉向不同方向收缩并对颞下颌关节施加压力。我们研究了每块肌肉的PCSA（肌肉力量的指标）与肌肉大小相对于身体大小的比例对颞下颌关节结构的影响。相对于身体大小的颞肌PCSA与颞下颌关节结构的相关性最高。当相对于身体大小的颞肌PCSA较大时，关节盂前突向尾侧突出，关节盂后突向头侧突出，关节盂前后突角间隔较小，表明髁突锁定在关节窝内以加强颞下颌关节。大多数食肉动物在切割食物时使用刀片状的裂齿。然而，当颞肌使用裂齿时会发生脱位。我们的结果表明，颞下颌关节得到加强以防止由颞肌引起的脱位。在鼬科中，具有向前突出的关节盂后突的颞下颌关节适合使用颞肌进行裂齿咬合。在猫科中，咬肌作用于裂齿的力量通过收紧颞下颌关节而转移到犬齿上。在犬科中，咀嚼肌的排列非常平衡，能够协同作用。因此，通过骨骼结构加强颞下颌关节是不必要的。
