Anatomical studies in the hyoid region of the mouse in term of evolutional importance.

The mouse hyoid region was studied in detail in term of its evolutional importance. A pair of small pyramidal-shaped "epiphyseal cornua" wedged between the body and the caudal cornua. It is suggested that the epiphyseal cornu is an independent element of the hyoid bone, and that it is not homologous with the typical hypohyal in other mammals. Just ventral of the tympanic bulla, there was a stylohyal, on which the "paroccipito-styloideus" and "paroccipitostylohyoideus" muscles (appellations by the authors) were attached. Ossification of the hyoid bone began at the attachments of the hyoid muscles, which acted synergically in tongue movement or swallowing. It is suggested that the ossification is triggered by the mechanical stress of the muscles in tongue movement or swallowing.