The most commonly recognized function of the diaphragm is the part it plays in the mechanism of inspiration and expiration. The diaphragm also acts as a dividing membrane that forms the floor of the chest cavity and the roof of the abdominal cavity. When in tone, the diaphragm prevents the abdominal viscera from being pushed into the thoracic cavity. It also acts as a pressor muscle during the acts of defecation and parturition.
The function that has been least emphasized and only recently recognized is the constrictor action of the muscle at the gastroesophageal junction. It was first described by Chevalier Jackson, and was called by him and his associates1 a pinch cock effect. I2 first encountered this phenomenon about four years ago during the course of certain experiments on the lung by using the transdiaphragmatic extraperitoneal route. Under certain conditions I encountered an acute distention of the stomach which