Muscle–tendon arrangement and innervation pattern of the m. flexor digitorum superficialis in the common marmoset (Callithrix jacchus), squirrel monkey (Saimiri sciureus) and spider monkey (Ateles sp.)

Abstract

The muscle-tendon arrangement of the m. flexor digitorum superficialis (FDS) varies among different primate groups. Recent developmental investigations revealed that the primordium of FDS emerges in the hand region first and relocates to the forearm later. The relationship between the diverse muscle-tendon arrangement and the characteristic developmental process of FDS is important for understanding the evolutionary changes of the FDS. Moreover, the innervation pattern cannot go unremarked when discussing the muscle homology and evolution. We examined the muscle-tendon arrangement and intramuscular nerve distribution of the FDS in three genera of Platyrrhini: three common marmosets (Callithrix jacchus), two squirrel monkeys (Saimiri sciureus) and two spider monkeys (Ateles sp.). We observed that the FDS consisted of multiple muscle bellies. The origin of the muscle bellies to digits II and V varied, whereas muscle bellies to digits III and IV consistently originated from the medial epicondyle. The muscle-tendon arrangement of the FDS differed among the three genera owing to the different origins of muscle bellies to digits II and V. In all the examined specimens, the muscle bellies to digits II and/or III were innervated by the direct nerve branches from the median nerve. However, the muscle bellies to digits IV and V never received direct nerve branches from the median nerve. Nerve branches within the belly to digit III extended into the belly to digit IV, and one nerve branch within the belly to digit IV extended into the belly to digit V. These consistent nerve distribution patterns suggest that different patterns of FDS muscle-tendon arrangement have changed from that of a common ancestral condition. It is plausible that the diverse origins of muscle bellies in the FDS are attributable to the difference in the destination for the relocation of the muscle bellies during developmental processes.

Evolutionary and terminological analysis of the flexor digitorum superficialis, interflexorii and palmaris longus muscles in kinkajou (Potos flavus) and crab‐eating racoon (Procyon cancrivorus)

“…In some primates, the FDS originates from the medial epicondyle of the humerus but is closely related to one of the humeral heads of the FDP, as described in S. leucopus (Vélez‐García et al., 2019), Callithrix jachuss , Saimiri sciureus and Ateles sp. (Emura et al., 2020). Even these authors (Vélez‐García et al., 2019; Emura et al., 2020) found the contribution of the median nerve to be in a similar pattern to that found in the IF of P. flavus and P. cancrivorus .…”

“…(Emura et al., 2020). Even these authors (Vélez‐García et al., 2019; Emura et al., 2020) found the contribution of the median nerve to be in a similar pattern to that found in the IF of P. flavus and P. cancrivorus .…”

“…In some primates, the FDS originates from the medial epicondyle of the humerus but is closely related to one of the humeral heads of the FDP, as described in S. leucopus (Vélez-García et al, 2019), Callithrix jachuss, Saimiri sciureus and Ateles sp. (Emura et al, 2020).…”

“…Several authors have reviewed the evolutionary derivation of the PL in mammals based on an analysis of its anatomical relationships and its innervation by the median or ulnar nerves (Jouffroy, 1971; Diogo & Abdala, 2010; Diogo & Wood, 2012; Kawashima et al., 2017). On the other hand, in primates, the innervation pattern has also been used to hypothesize the embryonic development of the FDS (Emura et al., 2020). Among the studies on P. flavus and P. cancrivorus , none report the innervation of the forelimb muscles, except for the palmaris longus internus muscle in P. flavus , which is innervated by the ulnar nerve (Beswick‐Perrin, 1871).…”

Gross anatomy of the gluteal and posterior thigh muscles in koalas based on their innervations

“…In addition, a muscle identification based on neuro-muscular specificity has enabled us to establish comparison with the eutherians, which has been considered difficult [ 28 ]. More numerous studies have been performed to clarify their gross anatomy among eutherian species [ 12 – 25 , 33 , 35 , 36 ]. As previously mentioned, comparison of anatomical findings in marsupials with those in eutherians would be an important insight into understanding the convergent evolution of mammals.…”