ABSTRACT
The diaphragm is unlike other muscles in its form and, therefore, in the basis for analysis of its action. Other muscles take the form of fascicles with attachments at either end and produce forces in straight lines that can be represented fairly accurately by vectors with point attachments on bones. Their bulk and direction are easily measured, and they are ftrm enough to retain the essence of their shape once resected. The diaphragm, on the other hand, is a very thin sheet that acts like a wet handkerchief when separated from its attachments. The force at its peripheral attachment is distributed along a line running around the whole interior of the rib cage. It has no insertion in the usual sense-its ftbers end in a central tendon that is not attached to anything rigid and may slip sideways as well as move up and down. The force at its central insertion is balanced largely by pressure distributed across its free surface.
