vii MECHANICS OF THE HEAET 187 



III. The active mechanical functions of the cardiac muscles 

 are intimately connected with the passive mechanical functions of 

 the semilunar and intracardiac valves, with which the arterial and 

 auriculo- ventricular orifices are respectively provided. 



The semilunar valves are fibrous membranes, forming pockets 

 attached to the edges of the arterial orifices, their concavity being- 

 turned upwards, and their curved free borders nearly always 

 provided with a nodule (corpus Arantii). These valves are regularly 

 arranged so that one segment corresponds with the posterior wall 

 of the aorta, and one with the anterior wall of the pulmonary 

 artery ; the remaining two closing with the former and converging 

 towards the anterior wall of the aorta, and the posterior wall of 

 the pulmonary artery. 



Each segment at the place where it is attached to the arterial 

 orifice abuts on a dilatation in the artery, which is known as the 

 sinus Valsalvae. 



Above the three reunited sinuses is the dilatation of the first 

 section of the two arteries, which is known as the bulbus 

 arteriosus. The aorta accordingly possesses one posterior and two 

 anterior lateral sinuses, a right and a left ; from each of these 

 arises a coronary artery, right and left. In the pulmonary artery 

 we have, on the contrary, one anterior and two posterior sinuses, 

 from which no arteries arise. 



Acquaintance with the anatomical form of these valves suffices 

 to show that their physiological function can be no other than to 

 inhibit or moderate the reflux of blood from the arteries to the 

 ventricles in diastole, while they readily permit the efflux from 

 ventricles to arteries during systole. From Galen to Vesalius, and 

 from Vesalius to our own day, it has been held that the opening of 

 the semilunar valves was the effect of the torrent of blood rushing 

 from the ventricles at systole, and that their closing was due to 

 the regurgitation of blood from the artery to the ventricle at the 

 commencement of diastole ; " uam obstaculuni ne quid penitus 

 regurgitaret effingere f uit impossibile " (Vesalius). Supposing that in 

 systole the semilunar valves are completely raised, so that they are 

 applied to the walls of the sinus Valsalvae and occlude the openings 

 of the coronary arteries (Thebesius, Briicke), or that they assume 

 the half-open position (Hamburger, Eiidinger, Hyrtl), then at the 

 beginning of diastole a greater or less reflux of blood must be 

 postulated, to bring the valves back from the open, or half-open, 

 position to that of complete closure. Ceradini (1871) was the first 

 who demonstrated that the office of the semilunar valves was not 

 to moderate, but entirely to inhibit the diastolic reflux. 



He repeated and perfected certain experiments of Eiidinger in 

 direct observation of the valves, by applying a sort of speculum 

 cordis to the cadaveric heart, while imitating the cardiac systole 

 and diastole, and was able to show : 



