Masticatory muscles of the great‐gray kangaroo (Macropus giganteus)

Abstract

The great-gray kangaroo (Macropus giganteus) belongs to the Diprotodontia suborder (herbivorous marsupials of Australia) of the order of marsupials. We dissected the masticatory muscles in the great-gray kangaroo and classified them based on their innervation. Three (two male and one female) adult great-gray kangaroos (M. giganteus), fixed with 10% formalin, were examined. The masseter muscle of the great-gray kangaroo was classified into four layers (superficial layers 1, 2, 3, and a deep layer), all innervated by masseteric nerves. Layer 1 of the masseter muscle was well developed and the deep layer inserted into the masseteric canal. The zygomaticomandibular muscle, which belongs to both the masseter and temporalis muscles, was innervated by both the masseteric nerve and posterior deep temporal nerve, and the temporalis muscle was innervated by the anterior and posterior deep temporal nerves. The medial pterygoid muscle, which was innervated by the medial pterygoid nerve, was divided into superficial and deep portions. The lateral pterygoid muscle was divided into superior and inferior heads by the buccal nerve. We propose that the relationship of the masticatory muscles in the kangaroo has evolved by passive anterior invasion of the deep layer of the masseter by the medial pterygoid muscle via the masseteric canal, associated with the development of an anteroposterior mode of mastication. Anat Rec 290: 382-388, 2007. 2007 Wiley-Liss, Inc.

Three dimensional digital reconstruction of the jaw adductor musculature of the extinct marsupial giantDiprotodon optatum

“…In kangaroos and wombats the superficial masseter is usually depicted as having two or more parts (Abbie, 1939; Crompton et al, 2008; Tomo et al, 2007). In kangaroos the more superficial layer originates from the small ventral tip of the masseteric process and inserts on the postero-ventral surface of the inflected mandibular angle.…”

“…The terminology used here was selected for its consistency with jaw muscle nomenclature used for marsupials (Abbie, 1939; Crompton et al, 2008; Davison & Young, 1990; Murray, 1998; Tomo et al, 2007; Turnbull, 1970; Warburton, 2009). The masseter muscle group includes three portions (superficial, deep and zygomaticomandibularis) based on their area of origin.…”

Developmental origins of species-specific muscle pattern

“…While much attention has been paid to the anatomical diversification of jaw bones and cartilages, few studies have identified developmental mechanisms that provide species- specific pattern to the closely associated musculature. Because the muscles that attach to the upper and lower portions of the jaw skeleton are integral for respiration and feeding, they have undergone dramatic evolutionary change in conjunction with the adaptive radiations of vertebrates (Bemis and Northcutt, 1991; Bowman, 1961; Cabuy et al, 1999; Edgeworth, 1935; Gosline, 1986; Haas, 2001; Holliday and Witmer, 2007; Smith, 1993; Tomo et al, 2007; Turnbull, 1970; Wood, 1965). For example, in groups such as pufferfish (Friel and Wainwright, 1997) and parrots (Toki*ta, 2004; Zusi, 1993), the number and organization of jaw muscles have been extremely modified, reflecting a high degree of plasticity in the developmental programs of the first (i.e., mandibular) arch (Schneider, 2005; Smith and Schneider, 1998).…”

Cranial biomechanics, bite force and function of the endocranial sinuses in Diprotodon optatum, the largest known marsupial

“…Each muscle group was modelled with two or three subdivisions based on published studies of marsupial jaw muscles (Turnbull, ; Murray, ; Tomo et al. ; Crompton et al. ; Warburton, ; Sharp, ; Sharp & Trusler, ).…”