The neurilemma (also known as neurolemma) is the outer layer of a Schwann cell which surround the axon of the nerve, covering the myelin sheath.
Neurilemmas are sometimes called a sheath of Schwann or Schwann's sheath because they are the outer layer or covering, like a sock, of Schwann cells. Schwann cells (also known as neurolemmocytes) are the main glial cells of the peripheral nervous system (PNS). The neurilemma, as the outermost layer, serves a protective function for peripheral nerve fibers. Schwann cells are either myelinating or nonmyelinating. Myelinating Schwann cells form around the axons of sensory and motor neurons to form the myelin sheath. Axons are myelinated by oligodendrocytes in the central nervous system therefore lacking neurilemma. A tumor that occurs in the neurilemma is called a neurilemoma.