294 PULMONARY MUCOUS TISSUE. 



bles that of a piston in the cylinder of a pump. This 

 muscle, it is true, has the form of an arch, and it has been 

 thought that in contraction its curve is straightened, and, in 

 this way, enlarges the vertical diameter ot the cavity of 

 which it forms the base. This base is represented to be 

 convex upwards during the repose of the muscle, and 

 flat during its contraction. It must, however, be remarked 

 that the curvature of the diaphragm exactly coincides with 

 that of the abdominal viscera, as, for example, on the right, 

 with that of the liver ; thus, when the muscle contracts, it 

 has no power to modify this convexity or curve, but can 

 only cause it to change its place from top to bottom, driving 

 the viscera before it in the same direction ; thus we see the 

 abdominal walls rise synchronically with each inspiratory 

 dilatation of the thorax. The diaphragm thus constitutes a 

 piston having a convex form, working in the cylinder of a 

 pump formed by the thoracic cage; in descending, however, 

 it does not act only on the vertical diameter of the thorax. 

 We must remember that its circular edge is inserted in the 

 ribs, that these latter are movable, and that, consequently, 

 when the arched centre of the diaphragm is directed down- 

 wards, its circular edge is sensibly elevated j in other words, 

 this muscle, like many others, has no really fixed points of 

 insertion, and its fibres, as they contract, present at one time 

 a relatively fixed point on the ribs, in order to lower both 

 the phrenic centre and the viscera, and on the viscera 

 (phrenic centre), in order to raise the ribs and the sternum. 



By this action the diaphragm forces the ribs forward and 

 outward, and, at the same tfme, dilates the thorax in its 

 antero-posterior and transverse diameters ; it may, therefore, 

 be said to act at once on the three diameters of the chest. 

 Most of the movements made in inspiration, especially in 

 young subjects and in man, 1 proceed from the diaphragm ; 

 women, after attaining the age of puberty, form an exception 

 to this rule, the respiratory type, instead of being abdominal 

 (diaphragmatic) or costo-inferior, being rather costo-superior. 

 This fact has, no doubt, some connection with the genital 



1 Paralysis of the diaphragm causes the greatest possible de- 

 rangement in all those functions which require that the thoracic 

 cage should be in perfect working order; although phonation is not 

 destroyed, the voice becomes extremely weak; coughing and sneez- 

 ing greatly hinder respiration. (See Duchenne (of Boulogne), 

 " De 1'Electrisation Localised. " Paris, 1872, p. 908 ) 



