Functional anatomy of the masticatory muscles in a caviomorph rodent, Cavia porcellus

Abstract

Guinea pigs (Cavia porcellus) and other caviomorph rodents are hystricognaths. In hystricognaths, there is a groove for the pars reflexa of the superficial masseter in the ventral border of the mandible (Druzinsky, 2007). In the guinea pig (C. porcellus) the tendon of the pars reflexa has a dense connective tissue sesamoid that permits the tendon to glide through the groove. These South American hystricognaths are also hystricomorphs. The zygomatico‐mandibularis muscle originates on the snout and converges on a tendon that runs posteriorly through the infraorbital foramen. The tendon runs over the bony root of the zygomatic arch and turns inferiorly, to insert at the anterior end of the masseteric groove. A second sesamoid is found in this tendon, which allows the tendon to glide over the root of the zygomatic arch. Each of these elaborations of the masticatory muscles is a pinnate muscle that curves around a bony structure, acting as a pulley, and permitting the muscle to be longer than similar muscles in other mammals.To analyze the mechanics of the caviomorph masticatory apparatus we are creating a 3D model of the skull, jaw, and masticatory muscles through contrast enhanced micro‐CT. The head of an adult guinea pig was soaked in a solution of called iodine potassium iodide (I2KI) for several weeks and then scanned at Northeast Ohio College of Medicine using the Scanco vivaCT micro‐CT. The Materialize Mimics® Innovation Suite will be used to segment the bones, teeth, and muscles to capture the detailed morphology. Modeling of length‐tension relationships and mechanical advantage suggests that the pulley mechanisms of the masseter complex permit these muscles to be long, which allows them to have long excursions and produce significant forces at large gapes.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.