Aspectos evolutivos sobre as origens, distribuições e ramificações dos nervos isquiáticos do tamanduá bandeira (Myrmecophaga tridactyla Linnaeus, 1758)

Abstract

The anteater (Myrmecophaga tridactyla) is one of the members of the Xenethra super order, a representative of the Pilosa Order and belonging to the Myrmecophagidae family. The sciatic nerve is a constituent of the lumbosacral plexus and is considered to be the largest nerve in the body of animals. This work has as its objective to describe the origin, distribution and ramifications of the sciatic nerve in giant anteater and in so doing provide anatomical data which can explain not only the evolutionary aspects but also provide important information as to related areas. For the present study three specimens of M. tridactyla were used, being prepared by perfusion of 10% formaldehyde via the femoral artery, for conservation and further dissection of specimens. The origin of right and left sciatic nerves in giant anteater come from the ventral ramification of lumbar spinal nerve number three and from number one, two and three of the sacral nerve. These are symmetrical in all animals studied. The distribution and ramification occurred in the superficial, medium and deep gluteus muscles and also in the twin, tensor fasciae latae, abductor cruris caudalis, biceps femoris, cranial and caudal semitendinosus and semimembranosus. It was observed that no homology of muscle innervations was retained throughout evolution, and that there was a rear end migration flow in the sciatic nerve in animals in more recent evolutionary scales. This is due to a reconfiguration of the lumbosacral plexus resulting from an increase in the number of lumbar vertebrae.