A clear understanding of the respiratory rôle of the diaphragm is necessary to analyze the respiratory movements in the thorax and abdomen. In former years the inspiratory excursion of the diaphragm was grossly exaggerated by estimating the excursion of the lower borders of the lungs as a measure of phrenic movement. These were misleading because the descent of the lung in the pleural sinus to an extent of 6 centimeters may be accomplished by the diaphragm descending or withdrawing from the thoracic wall only a distance of 1 centimeter.
The inspiratory descent of the anterior hepatic border is an exaggeration of phrenic movement because the liver rotates on a transverse axis during inspiration and is not depressed in toto during inspiration. This axis of rotation is marked by the posterior hepatic border or that liver portion which is not covered by peritoneum. This part of the liver