Evolutionary aspects on the origin, distribution and ramifications of the ischiadicus nerve in the giant anteater (Myrmecophaga tridactyla)

L.A Ribeiro,L.P Iglesias,H.I.R Magalhães,Y.H Paula,L.A Santos,R.A.C Barros,F.O.C Silva,Z Silva

doi:10.1590/1678-4162-10639

Abstract

ABSTRACT This work aimed to describe the origin, distribution, and ramifications of the ischiadicus nerve in the giant anteater and to provide anatomical data which could explain not only the evolutionary aspects but also provide important information for other related works. For the present study, four specimens were used, prepared by perfusion of 10% formaldehyde solution via the femoral artery, for conservation and dissection. The origin of the right and left ischiadicus nerves in the giant anteater from the ventral ramification of the third lumbar (L3) and the first (S1), second (S2), and third (S3) sacral spinal nerves. These nerves were symmetrical in all animals studied. The distribution and ramification occurred to the superficial, middle, and deep gluteal, gemelli, piriform, quadratus femoris, tensor fasciae latae, caudal crural abductor, cranial and caudal parts of the biceps femoris, adductor, semitendinous, and cranial and caudal parts of the semimembranous muscles. Based on the origins of the ischiadicus nerves, there is a caudal migration in the nerve location in animals in a more recent position on the evolutionary scale due to reconfiguration of the lumbosacral plexus, resulting from the increase in a number of lumbar vertebrae. There is no complete homology of the muscle innervation.

Highlights

The giant anteater, Myrmecophaga tridactyla, is a member of the placental superordem Xenarthra, representing the order Pilosa and belonging to the family Mymercophagidae (Wilson and Reeder, 2005)
Ventral macrophotography of the left antimere showing the course of the ischiadicus nerve (I) through the major ischiatic foramen, which is bounded by the internal obturator muscle (IO), deep gluteal muscle (DG), sacrotuberous ligament (ST), and the major ischiatic incisures (MI)
In our study we considered that the M. tridactyla specimens had no cranial and caudal gluteal nerves, but a nerve trunk consisting of an ischiadicus plexus, resulting from the union of the ventral branches of the third (L3) lumbar and first (S1), second (S2) and third (S3) sacral spinal nerves

Summary

Introduction

The giant anteater, Myrmecophaga tridactyla, is a member of the placental superordem Xenarthra, representing the order Pilosa and belonging to the family Mymercophagidae (Wilson and Reeder, 2005). The Xenarthra are restricted to the New World in a determined geographic area and are morphologically isolated (Engelmann, 1985) from the rest of the placental mammals, which likely occurred during the Cretaceous period, as long as 106 million years ago (Delsuc et al, 2001). According to Carvalho-Barros et al (2003), the evolutionary aspects of the posture and locomotion are understood through the study of the neural plexus, with the lumbosacral plexus being of great importance as it is the representative of the origin of the pelvic member nerves. It is extremely important to know the origin, distribution, and ramification of the ischiadicus nerve because it is considered vulnerable to several lesions, especially a few centimeters caudal to the femur, between the biceps femoris and semimembranous muscles (Dyce et al, 2004). Symptoms from ischiadicus nerve lesions include insensitivity and motor dysfunction on the gluteus area, thigh and leg of the affected limb (Guimarães et al, 2005)

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