SOUNDS OF THE HEART. 



119 



the other forms a double curve or festoon just below the 

 free border. Each of these cords is attached by its outer 

 extremities to the outer end of the free margin of its valve, 

 and in the middle to the corpus Arantii ; they thus enclose 

 a lunated space from a line to a line and a half in width, 

 in which space the substance of the valve is much thinner 

 and more pliant than elsewhere. When the valves are 

 pressed down, all these parts or spaces of their surfaces 

 come into contact, and the closure of the arterial orifice is 

 thus secured by the apposition not of the mere edges of the 

 valves, but of all those thin lunated parts of each, which 

 lie between the free edges and the cords next below them. 

 These parts are firmly pressed together, and the greater 

 the pressure that falls on them, the closer and more secure 

 is their apposition. The corpora Arantii meet at the centre 

 of the arterial orifice when the valves are down, and they 

 probably assist in the closure ; but they are not essential 

 to it, for, not unfrequently, they are wanting in the valves 

 of the pulmonary artery, which are then extended in larger, 

 thin, flapping margins. In valves of this form, also, the 

 inlaid cords are less distinct than in those with corpora 

 Arantii ; yet the closure by contact of their surfaces is not 

 less secure. 



Sounds of the Heart. 



When the ear is placed over the region of the heart, two 

 sounds may be heard at every beat of the heart, which 

 follow in quick succession, and are succeeded by a pause 

 'or period of silence. The first sound is dull and pro- 

 longed ; its commencement coincides with the impulse of 

 the heart, and just precedes the pulse at the wrist. The 

 second is a shorter and sharper sound, with a somewhat 

 flapping character, and follows close after the arterial pulse. 

 The period of time occupied respectively by the two sounds 

 taken together, and by the pause, are almost exactly equal. 



