On Muscular Motion and Animal Spirits 287 



themselves, they are carried in their contraction 

 towards the centre of that space which they 

 surround. 



CHAPTER VII 



OF THE CONTRACTION OF THE DIAPHRAGM. ALSO, 

 OF THE PULSATION OF THE HEART, INCIDEN- 

 TALLY, OF THE PALPITATION OF THE HEART. 

 ALSO, OF THE MOTION OF ANIMALS WHEN THEY 

 RAISE THEMSEL VES ALOFT 



In the last chapter we have spoken of the motion of 

 contracting muscles in general, and specially of the 

 tiexor muscles. Let us now further consider more 

 closely how the diaphragm moves when it contracts, 

 also in what manner the pulsation of the heart is 

 produced ; and, finally, how the extensor muscles, by 

 means of which jumping is effected, contract. 



First, then, as to the contraction of the diaphragm, 

 although I have discoursed of it in my recently 

 published treatise On Respiration,^ still there are some 

 things which may be added here. 



In the first place, then, I aflBrm as indubitable that 

 if a curved surface, the circumference of which is on 

 all sides fixed to an immovable part, undergoes 

 contraction, it will all round be carried towards the 

 immovable part, and the curved surface will ap- 

 proximate to a plane but will never go beyond the 

 plane ; as is shown in Plate III., Fig. 5, in which let 

 b, a, c be the curved surface and b and c its fixed 

 ends. As it contracts it will be brought towards the 

 plane 3, ^, c. So that the contracted surface b, d^ c, 

 that is to say its middle point d^ is nearer to the 



