VEINS AND HEART. 



much in the same way as in the veins ; but in 

 this case there are three such cups, and their 

 three flaps meet at a point in the centre of the 

 vessel. One of them is shown at G, and beside 

 it a small portion of each of the others. 



FlG. 63.- MEGHAN ISM OF THE HEART-VALVES. 



The ventricle having emptied itself by 

 squeezing itself together, it now actively dilates 

 to receive the next charge of blood, and in con- 

 sequence of this dilatation there is very little 

 pressure for the auricle B to overcome in empty- 

 ing itself into the ventricle. It consequently 

 needs no great strength and has no great 

 thickness of muscle, and no special valves to 



295 



