288 Mayow 



ends, b and c, than the middle point, a^ of the surface 

 not yet contracted, but that surface, however much 

 contracted, can never go beyond the plane, 3, c, as the 

 line, 3, e^ c, is the shortest between the ends, 3, c. 



These things being granted, we assert that the 

 diaphragm in its contraction is moved towards a 

 plane ; in other words, when it contracts, it goes 

 towards the cavity of the abdomen, that is, outwards 

 and downwards. For it is known from anatomical 

 observation that the form of the diaphragm is curved, 

 and that its concave surface or sinus looks towards 

 the belly ; but now as any curved surface whatsoever 

 moves, in contracting, towards a plane, that is, towards 

 the region to which its concave surface looks, and as 

 the parts of the abdomen to which the concave 

 surface of the diaphragm looks are relatively to it, 

 inferior and exterior, it necessarily follows that when 

 the diaphragm, in its contraction, moves towards 

 them, in its contracted state it goes downwards and 

 outwards. And besides, this can be seen in vivi- 

 sections by simple inspection. In this connection I 

 am much astonished that the eminent Dr Willis, in 

 his Answer to Dr Highmore^ has expressed the 

 opinion, " That the diaphragm in violent inspiration, 

 such as sometimes occurs in the case of dying 

 persons, descends beyond the plane and becomes very 

 convex towards the intestines." For this does not 

 seem very likely : for it is not " possible that such a 

 descent of the diaphragm should be caused by the 

 lungs taking a long inspiration," as the distinguished 

 author supposed, inasmuch as the inspiration and 

 the swelling of the lungs are caused by the descent 

 of the diaphragm and the dilatation of the chest. 

 But the lungs never cause the descent of the diaphragm, 

 but in all cases follow its motion, as we have else- 



