The vagina may also be referred to as the birth canal in the context of pregnancy and childbirth. Although by its dictionary and anatomical definitions, the term vagina refers exclusively to the specific internal structure, it is colloquially used to refer to the vulva or to both the vagina and vulva. Using the term vagina to mean "vulva" can pose medical or legal confusion; for example, a person's interpretation of its location might not match another's interpretation of the location. Medically, one description of the vagina is that it is the canal between the hymen (or remnants of the hymen) and the cervix, while a legal description is that it begins at the vulva (between the labia). It may be that the incorrect use of the term vagina is due to not as much thought going into the anatomy of the female genitals as has gone into the study of male genitals, and that this has contributed to an absence of correct vocabulary for the external female genitalia among both the general public and health professionals. Because a better understanding of female genitalia can help combat sexual and psychological harm with regard to female development, researchers endorse correct terminology for the vulva. Structure Gross anatomy The human vagina is an elastic, muscular canal that extends from the vulva to the cervix. The opening of the vagina lies in the urogenital triangle. The urogenital triangle is the front triangle of the perineum and also consists of the urethral opening and associated parts of the external genitalia. The vaginal canal travels upwards and backwards, between the urethra at the front, and the rectum at the back. Near the upper vagina, the cervix protrudes into the vagina on its front surface at approximately a 90 degree angle. The vaginal and urethral openings are protected by the labia. When not sexually aroused, the vagina is a collapsed tube, with the front and back walls placed together. The lateral walls, especially their middle area, are relatively more rigid. Because of this, the collapsed vagina has an H-shaped cross section. Behind, the upper vagina is separated from the rectum by the recto-uterine pouch, the middle vagina by loose connective tissue, and the lower vagina by the perineal body. Where the vaginal lumen surrounds the cervix of the uterus, it is divided into four continuous regions (vaginal fornices); these are the anterior, posterior, right lateral, and left