The diaphragm is the thin, dome-shaped muscular partition which separates the cavity of the abdomen from that of the chest. It is of great importance in respiration, playing the chief part in ﬁlling the lungs. During deep respiration its movements are responsible for 60 per cent of the total amount of air breathed, and in the horizontal posture, or in sleep, an even greater percentage.
The description ‘diaphragm’ is also used for the hemispherical rubber (‘dutch’) cap used in conjunction with a chemical spermicide as a contraceptive. It ﬁts over the neck of the uterus (cervix) inside the vagina. (See CONTRACEPTION.)