Lamination of the Masticatory Muscles in the Kangaroo According to Their Innervation

Abstract

Summary: An analysis of the laminations of the masseteric, zygomaticomandibular and temporalis muscles of the Red Kangaroo (Macropus Rufus) and all of the masticatory muscles of the Eastern Gray Kangaroo (Macropus Giganteus) was carried out based on their innervation. The masseteric muscle was divided into superficial and deep layers; the superficial layer was further subdivided into three laminae from the rostro-lateral portion to caudo-internal portion. The deep layer was divided into lateral, caudo-internal and rostro-internal laminae. The zygomaticomandibular muscle which was located between the masseteric and temporal muscles was divided into lateral, internal and rostral laminae, on the basis of its innervation. The lateral and internal laminae were innervated by the nerve which arises between the masseteric nerve and the posterior deep temporal nerve. A small rostral portion of the muscle was innervated by masseteric nerves, which passed through the internal lamina of the deep layer of the masseteric muscle. The temporalis muscle was innervated by an anterior deep temporal nerve and posterior deep temporal nerve. Only the most rostrointernal lamina of the temporalis muscle was innervated by the anterior deep temporal nerve. The anterior deep temporal nerve and lateral pterygoid nerve had a common trunk. We believe that the rostro-internal lamina was closely related to the lateral pterygoid muscle. The lateral pterygoid muscle displayed one lamina, whereas the medial pterygoid muscle was divided into internal and lateral laminae. The lateral lamina was further divided into rostro-internal and caudo-lateral laminae.

Comparative Jaw Muscle Anatomy in Kangaroos, Wallabies, and Rat‐Kangaroos (Marsupialia: Macropodoidea)

“…The correlation between feeding strategy and morphology in kangaroos has been investigated by several researchers, and the results have indicated differences in dental morphology and behavior associated with the feeding types (Sanson, 1979, 1980, 1989; Hume, 1982; McArthur and Sanson, 1988; Lentle et al, 1998, 2003). Studies of the masticatory muscles, however, apparently indicate a basic conservatism (Parsons, 1896; Windle and Parsons, 1897; Heighway, 1939; Yoshikawa and Suzuki, 1965; Sanson, 1980; Morton, 1981; Lentle et al, 1998; Nakajima et al, 2000; Tomo et al, 2007). With the notable exception of the work by Sanson (1980, 1989), and a paper by Lentle et al (2003), there have been no comparative studies of kangaroo jaw musculature between genera or of different feeding types.…”

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

“…But we can not say for certain whether the estimation is collect or not because of no performs of functional analysis. In previous studies of the lamination of the masseter deep layer in humans, dogs and kangaroo, no one has observed oblique structures (Tomo et al, 1993;Nakajima et al, 1998Nakajima et al, , 2000. Only the deep nerve layer of the P. cinereus's masseter displays four oblique laminae.…”

“…According to the distribution pattern of the masticatory muscles in the pig, Koppe et al (1988) suggested that the paths of the nerves and the position of the aponeuroses were not related. Tomo et al (1993), Nakajima et al (1998Nakajima et al ( , 2000 and Nakajima (2001) have classified the masticatory muscles in dog, kangaroo and humans according to their innervations and proposed that this provides a better insight into phylogenetic relationships and function. Davison et al (1990) described the structure of the P. cinereus masticatory muscle but they did not recognize the lamination of the medial pterygoid muscle.…”

“…In fact, nerves distributed into muscle bundles from other muscle layers often penetrate tendons or aponeuroses (Koppe et al, 1988;Schumacher et al, 1974;Lau et al, 1974;Widmer, 1997). Some researchers have noted specific nerve distributions within these muscles (Akita et al, 2000;Nakajima, 2001;Nakajima et al, 1998Nakajima et al, , 2000Shimokawa et al, 1988Shimokawa et al, , 1999Tomo, 1990;Tomo et al, 1993;Watanabe, 1997). Nerves control the action of muscles, so improved understanding about innervation patterns in the masticatory muscles is important in the consideration of muscle function.…”

The Laminar Structure of the Common Opossum Masseter (Didelphis marsupialis)

“…However, the reverse laminar theory is not an accepted theory at present. Later, Tomo (1990), Watanabe (1997) and Nakajima et al (2000) attempted to separate the masseter into the layers from the innervations. However, no new theory superior to the laminar structure theory has as yet been reported.…”