Numerous studies have investigated how the skeletal morphology is related to feeding behaviour (Christiansen and Adolfssen 2005; Wroe et al. 2005; Christiansen and Wroe 2007; Ellis et al. 2009; Koyabu and Endo 2009; Koyabu et al. 2009; Koyabu and Endo 2010), although remarkably few studies have focused on the architecture of masticatory muscles from which bite forces are produced. In this regard, the quantification of physiological cross-sectional areas (PCSA) of muscle is critical for estimation of bite forces. PCSA is generally proportional to and regulates maximum force-generating capacity (Santana et al. 2010). To date, PCSA of masticatory muscles are reported for bats (Burke et al. 1974; Santana et al. 2010), primates (Weijs and Hillen 1985; Antón 1999; Anapol et al. 2008), sloths (Naples 1985), rodents (Weijs and Dantuma 1975; Weijs 1980; Druzinsky 2010), rabbits (Weijs and Dantuma 1980), and pigs (Herring 1980, 1985). Since quantification of muscle PCSA is critical to estimate bite forces in animals, and since yet little is understood about the relationship between the variation of masticatory muscle PCSA and diversity in feeding behavior among mammals, further accumulation of knowledge on masticatory muscle PCSA is highly needed.