medullary sheath: a layer of myelin encasing (and insulating) the axons of medullated nerve fibers
sheath: an enveloping structure or covering enclosing an animal or plant organ or part
california personality inventory: a self-report personality inventory originally derived from the MMPI; consists of several hundred yes-no questions and yields scores on a number of scales including dominance and self acceptance and self control and socialization and achievement etc.