372 RESPIRATION. 



subject of numerous experiments by the earlier physiologists, 

 who were greatly interested in the minutiae of the action of 

 the diaphragm, and other muscles, in respiration. Its gal- 

 vanization produces convulsive contractions of the diaphragm, 

 and its section paralyzes the muscle almost completely. It 

 was noticed by Lower, that after section of both phrenic 

 nerves the movements of the abdomen were reversed, and it 

 became retracted in inspiration. 1 This is explained and illus- 

 trated by voluntary suspension of the action of the diaphragm, 

 and exaggeration of the costal movements. As the ribs are 

 raised, the atmospheric pressure causes the diaphragm to 

 mount up into the cavity of the thorax, and of course the 

 abdominal organs follow. 



From the great increase in the capacity of the chest pro- 

 duced by the action of the diaphragm, and its constant and 

 universal action in respiration, it must be regarded as by far 

 the most important and efficient of the muscles of inspiration. 



Hiccough, sobbing, laughing, and crying are produced 

 mainly by the action of the diaphragm, particularly hic- 

 cough and sobbing, which are produced by spasmodic con- 

 tractions of this muscle, generally beyond the control of the 

 will. 



Action of the Muscles which elevate the Ribs. Scalene 

 Muscles. In ordinary respiration, the ribs and the entire 

 chest are elevated by the combined action of a number of 

 muscles. The three scalene muscles are attached to the cervi- 

 cal vertebrae and the first and second ribs. These muscles, 

 which act particularly upon the first rib, must elevate with 

 it, in inspiration, the rest of the thorax. The articulation of 

 the first rib with the vertebral column is very movable, but 

 it is joined to the sternum by a very short cartilage, which 

 allows of very little movement, so that its elevation necessa- 

 rily carries with it the sternum. This movement increases 

 both the transverse and antero-posterior diameters of the 



1 BERARD, Cours de Physiologic, Paris, 1851, tome iii., p. 245. 



