The Superficial Masseter and Gape in Mammals

TLDR

Gape depends on the relative distances of the superficial masseter’s origin and insertion from the jaw joint and the angle between them. The study develops a geometrical model linking gape to the orientation of the superficial masseter. The model is based on geometric assumptions about muscle orientation relative to the jaw joint, which are explicitly examined. Measurements on diverse placental skulls confirm the model’s predictions, and the approach can be extended to other adductor muscles.

Abstract

A geometrical model is developed, relating gape to the orientation of the superficial masseter muscle. The degree to which the muscle must stretch depends on relative distances of its origin and insertion from the craniomandibular joint and the angle between these line segments. Assumptions of the model are considered. Measurements on a variety of placental skulls demonstrated the validity of predictions derived from the model. This method of analysis can be applied to other adductor muscles.