104 



THE CIRCULATION. 



the muscular substance of the ventricle. Availing himself of 

 a method of dissection hitherto appar- 

 ently overlooked, namely, that of mak- 

 ing vertical sections (Fig. 39) through 

 various parts of the tendinous rings, 

 he has been enabled to show clearly 

 that the aorta and pulmonary artery, 

 expanding towards their termination, 

 are situated upon the outer edge of the 

 thick upper border of the ventricles, 

 and that consequently the portion of 

 each semilunar valve adjacent to the 

 vessel passes over and rests upon the 

 muscular substance being thus sup- 

 ported, as it were, on a kind of muscu- 

 lar floor formed by the free border of 

 vertical section through the the ventricle. The result of this ar- 

 aorta at its junction with the ran g emen t will be that the reflux of 

 It r" I', s^r ol the blood will be most efficiently sus- 

 valve, s. Section of ventricle, tamed by the ventricular wall. 1 



The effect of the blood's pressure on 



the valves is, as said, to cause their margins to meet in three 

 lines radiating from the centre to the circumference (7 and 8, 

 Fig. 38). The contact of the valves in this positton, and the 

 complete closure of the arterial orifice, are secured by the pe- 

 culiar construction of their borders before mentioned. Among 

 the cords which are interwoven in the substance of the valves, 

 are two of greater strength and prominence than the rest ; of 

 which one extends along the free border of each valve, and 

 the other forms a double curve or festoon just below the free 

 border. Each of these cords is attached by its outer extremi- 

 ties to the outer end of the free margin of its valve, and in the 

 middle to the corpus Arantii; they thus inclose 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 luna- 

 ted parts of each, which lie between the free edges and the 

 cords next below them. These parts are firmly pressed to- 

 gether, and the greater the pressure that falls on them, the 



1 Mr. Savory's preparations, illustrating this and other points in 

 relation to the structure and functions of the valves of the heart, are 

 in the museum of St. Bartholomew's Hospital. 



