1 90 Mayow 



expanded. And here, following not so much the 

 authority of writers as the truth, I shall state briefly 

 what the thing itself teaches. 



The received opinion is that of the intercostal 

 muscles, only the external serve to dilate the chest, 

 while the internal, on the other hand, contract it. 

 But it seems to me more reasonable to suppose that 

 the chest is dilated simultaneously by both. And 

 that this may be better understood I shall premise 

 the following observations. 



We may affirm that the raising of the ribs dilates 

 the space within the chest and that their depression 

 diminishes it. For we suppose here (what any one 

 may see in a skeleton) that the ribs (especially the 

 lower, which contribute most to the dilatation of the 

 chest) are not articulated to the spine and sternum at 

 right angles, but that the angles below the ribs are a 

 little less than right angles ; so that if a rib is raised, 

 its articulations with the spine and sternum will 

 approach to right angles. We assert further that 

 the chest is dilated by the ribs when raised to right 

 angles. For let us imagine a number of arches lying 

 upon a plane, as represented in Plate II., Fig. i ; while 

 they remain in this position there is no space at all 

 between the arches and the plane, for we suppose that 

 thev are in mutual contact. If, however, the said 

 arches are raised somewhat above the plane, there is 

 a certain intervening space, and, in proportion as they 

 rise towards right angles, the spaces between them 

 and the plane become greater. Now it is precisely 

 the same in the case of the chest. For let a, in the 

 figure be the spine; 3, the sternum ; and c, c, c, r, the 

 ribs. Let the plane between the spine and the 

 sternum be the mediastinum, or any imaginary plane 

 dividing the thorax into equal parts : how much the 



