Final answer:
A Hegar dilator is the surgical instrument used to dilate the cervix, which is necessary for certain gynecological procedures.
Step-by-step explanation:
The instrument used to dilate the cervix is known as a Hegar dilator. It is commonly used in gynecological procedures to gradually dilate the cervix. The Hegar dilator is a smooth, round, tapered instrument that comes in various sizes and is used to gently enlarge the cervical opening during procedures such as insertion of an intrauterine device (IUD), abortion, or during the early stages of labor to facilitate delivery.