1723. These constitute the inward human membranes, which occupy much space, so there are accordingly many of them, or troops of them. These membranes are no different, and perform no other use than that of being passive forces that carry out whatever the active forces communicate. These were believed to constitute the pleura that surrounds the thoracic chamber, penetrating through the pericardium to the lungs, and then extending across to the pharynx and the larynx, which is the organ of speech-as also are the lungs, which the pleura encircles and of which it forms the covering.