A generally funnel-shaped protective disposable sheath is provided for use with a muscle monitor of the kind including a compressible-expansible elongated bulb insertable into a body cavity and a generally annular flange of greater diameter than the bulb adjacent one end of the bulb for limiting the extent of penetration of the bulb into the body cavity. The sheath is made of flexible elastomeric material and includes an anterior end portion which is adapted to fit over the bulb. The anterior portion is of elongated tubular configuration having a closed free end and an opposite end which is open and merges into a generally cup-shaped posterior portion of enlarged diameter adapted to overlie that surface of the muscle monitor flange which faces the bulb.
