The sciatic nerve forms from the merger of the fourth and fifth lumbar nerves with the first, second, and third sacral nerves. From the lower back, the sciatic nerve runs inferiorly into the gluteal region and into the posterior of the femoral region of the leg. Smaller individual nerves branch off from the sciatic nerve to innervate our thigh muscles and skin. At the inferior end of the femoral region, the sciatic nerve branches off into the tibial and common fibular nerves, which continue carrying nerve signals into the lower legs and feet.
Mammals – which appear in the fossil record after the first fishes, amphibians, and reptiles – are the only vertebrates to possess the evolutionarily recent, outermost part of the cerebral cortex known as the neocortex .  The neocortex of monotremes (the duck-billed platypus and several species of spiny anteaters ) and of marsupials (such as kangaroos , koalas , opossums , wombats , and Tasmanian devils ) lack the convolutions – gyri and sulci – found in the neocortex of most placental mammals ( eutherians ).  Within placental mammals, the size and complexity of the neocortex increased over time. The area of the neocortex of mice is only about 1/100 that of monkeys, and that of monkeys is only about 1/10 that of humans.  In addition, rats lack convolutions in their neocortex (possibly also because rats are small mammals), whereas cats have a moderate degree of convolutions, and humans have quite extensive convolutions.  Extreme convolution of the neocortex is found in dolphins , possibly related to their complex echolocation .
The common symptoms of PACNS are: confusion, headache and personality change. Other symptoms noted are: seizures, bleeding in the head, coma and vision loss . Occasionally patients can develop symptoms similar to stroke, which can involve a wide range of neurological symptoms, such as mobility and balance problems, speech difficulties, memory loss, hearing loss, cognitive problems, difficulties controlling arms and legs, fatigue, and bladder and bowel incontinence. Usually symptoms appear over several months but can occur quickly. Some forms of CNS vasculitis can closely mimic multiple sclerosis.