Lamination of the Masticatory Muscles in the Phascolarctos cinereus (Koala) According to Their Innervations

Abstract

Summary:The masticatory muscles are usually classified into four groups: masseter, temporalis, lateral pterygoid and medial pterygoid. The communicating muscle bundle between the temporalis and masseter called the zygomaticomandibular muscle exists. The laminations within these muscles are commonly separated by aponeuroses. Nerves control the action of muscles, so improved understanding about innervation patterns in the masticatory muscles is important in the consideration of muscle function. In this study, we focus on the relationships between the nerves supply and the lamination of masticatory muscles in Phascolarctos cinereus (Koala).The masseter muscle consists of superficial and deep muscle layers. The superficial muscle layer of the masseter muscle is divided into rostro-lateral and caudo-internal nerve layers. The deep muscle layer of the masseter muscle is divided into rostral, rostro-lateral, medial and caudo-internal nerve layers. The nerves that innervate the zygomaticomandibular muscle are distributed to the lateral area of the coronoid process. The temporalis muscle was divided into internal layer of the coronoid process, a lateral layer of the coronoid process and a posterior layer by the nerve distribution pattern. The medial pterygoid muscle divided into rostro-internal, medial and caudo-lateral nerve layers.

Oral health in South East Queensland Koalas: Prevalence of periodontal disease and other pathologies

“…The deep masseter, temporalis superior and medial pterygoid muscles work in unison to produce a powerful bite force allowing the koala to cut and chew eucalyptus leaves using lateral anisognathic and anteroposterior isognathic jaw movements effectuated by the superficial masseter (Davison andYoung, 1990, Nakajima andTownsend, 2009). Route for blood vessels…”

“…Previous investigations of the koala oral cavity have focused on evolutionary aspects (Grand, 2001), lingual papillae (Kobayashi et al, 2003), parotid and mandibular salivary gland composition and secretion rates (Beal, 1990b, Beal, 1991, Beal, 1990a, oral microbiology and disease (Bird, 2002, Mikkelsen et al, 2008b, Mikkelsen et al, 2008a, eruption sequence (Thomas, 1887), rostral anatomy (Kratzing, 1984), masticatory muscles (Nakajima and Townsend, 2009), jaw movements (Davison and Young, 1990), functional dental morphology (Lanyon and Sanson, 1986b), and development of predictive chronological age classes (Eberhard, 1972, Gordon, 1991, Young, 1990b, Lanyon and Sanson, 1986a, Martin, 1981, Martin and Handasyde, 1999.…”

The Development of an Oral Health Charting System for Koalas(Phascolarctos Cinereus)

“…Oral health status on the koalas has been lacking from the published pages of journals apart from two earlier reports. 8,9 Previous investigations of the koala oral cavity have focussed on evolutionary aspects, 10 lingual papillae, 11 parotid and mandibular salivary gland composition and secretion rates, 12,13 oral microbiology and disease, 14,15 eruption sequence, 16 rostral anatomy, 17 masticatory muscles, 18 jaw movements, 19 functional dental morphology, 20 and development of predictive chronological age classes. [21][22][23][24][25][26] The koala has a unique specialized masticatory physiology with eight muscles of mastication including a wide massetertemporalis muscle complex.…”

“…19 The deep masseter, temporalis superior, and medial pterygoid muscles work in unison to produce a powerful bite force allowing the koala to cut and chew eucalyptus leaves using lateral anisognathic and anteroposterior isognathic jaw movements effectuated by the superficial masseter. 18,19 A fused symphysis and large medially inflected mandibular process separates them from being typical herbivorous species. 27 Hind gut digestion of the vegetation provides the nutritious requirements after comminution into fine particulates by the bunoselenoid molariform teeth.…”