The lateral-costal method may be described as the system of "fixation of the diaphragm, and expansion of the sidewalls of the chest." 
In explanation of this it may be useful to remark, that many teachers speak of the "inversion" or "lowering" of the diaphragm when inhaling breath. The diaphragm is a muscular shield extending across the body, separating the breathing apparatus from the digestive organs, and forming the floor of the lungs. A. Lungs. B. Diaphragm.
In other words, the expansion of the lungs when full, according to this method, forces the diaphragm from a convex to a concave position, thereby allowing room for lung-expansion, at the same time pressing down the viscera. Dr. Hulbert, in his able treatise on breathing, says, "It is a physical impossibility for the diaphragm to be lowered and the ribs expanded sideways at one and the same time." Therefore, as the system of lowering the diaphragm makes it necessary, as the breath is expended, for it to resume its original position, and as there is no direct way to govern the even movement of this muscular shield, it often trembles, and, communicating this trembling to the lungs (which are attached to it ), it produces that nervous, bleating vibrato, so distressing to hear. It is obvious, then, that in fixing the diaphragm we gain doubly; first, by obtaining a greater "side-rib" expansion; secondly, by avoiding the tremolo.
Exercise 1.
Stand steady on both feet, with chest expanded; slightly draw in front wall of abdomen (this fixes the diaphragm),
