Deguchi T, Takemura A, Suwa F
Department of Anatomy, Osaka Dental University, 8-1 kuzuhahanazono-cho, Hirakata City, Osaka, 573-1121, Japan.
Okajimas Folia Anat Jpn. 2001 Mar;77(6):233-42. doi: 10.2535/ofaj1936.77.6_233.
Using three heads of the common opossum (Didelphis marsupialis), which may be considered to have a primitive mammalian form and therefore be appropriate for this study, the laminar structure of the masseter was investigated. We also attempted a comparative anatomical study of the relationships of food habits to the laminar structures of the masseter, zygomatic arch and mandibular ramus. In the common opossum masseter, a total of six layers, the primary and secondary sublayers of the superficial layer, the intermediate layer, and the primary, secondary and third sublayers of the deep layer as a proper masseter, were observed. These layers showed a typical reverse laminar structure, with the layers of tendons and muscles alternating. The maxillomandibularis and zygomaticomandibularis muscles were observed in one layer each, as an improper masseter. The laminar structure of the common opossum masseter was shown to be more similar to that of carnivorous placental animals than that of the herbivorous red kangaroo, a similar marsupial. In regard to the number of layers in the laminar structure of the masseter, the results of both this study and those of our predecessors' showed that differences in food habits affect the deep layer in the proper masseter of marsupials and placental mammals, and that of the maxillomandibularis muscle of placental mammals in the improper masseter.
利用三只北美负鼠（Didelphis marsupialis）进行研究，这种动物可被认为具有原始的哺乳动物形态，因此适合此项研究，我们对咬肌的分层结构进行了研究。我们还尝试对饮食习惯与咬肌、颧弓和下颌支的分层结构之间的关系进行比较解剖学研究。在北美负鼠的咬肌中，共观察到六层，即表层的初级和次级亚层、中间层以及深层作为正常咬肌的初级、次级和第三亚层。这些层呈现出典型的反向分层结构，肌腱层和肌肉层交替出现。颌上颌肌和颧颌肌各在一层中被观察到，属于异常咬肌。结果表明，北美负鼠咬肌的分层结构与肉食性胎盘动物的更为相似，而与草食性的红袋鼠（一种类似的有袋动物）不同。关于咬肌分层结构中的层数，本研究结果以及我们前人的研究结果均表明，饮食习惯的差异会影响有袋动物和胎盘哺乳动物正常咬肌的深层，以及胎盘哺乳动物异常咬肌中颌上颌肌的深层。
