MOTION OF THE HEART AND BLOOD 



some distance from the heart, have a more thick, 

 powerful, and muscular heart, as is obvious and 

 necessary. On the contrary, those whose structure 

 is more slender and soft have a more flaccid, less 

 massive, and weaker heart, with few or no fibers 

 internally. 



Consider likewise the function of the sigmoid 

 valves. These are so made that blood once received 

 into the ventricles of the heart, or sent into the 

 pulmonary artery or aorta, can not regurgitate. 

 When they are raised and tightly joined, they form 

 a three pointed line, like the bite of a leech, and the 

 more tightly they are forced shut, the more do they 

 block the reflux of blood. 



The tricuspids are like gate-keepers at the point 

 of inflow from the vena cava and pulmonary vein, 

 so that the blood, v/hen strongly propelled, may 

 not escape back into them. They are not present 

 in all animals, for the reason stated, nor do they 

 seem to have been made with the same efficiency in 

 those in which they are found. ° In some they are made 



^ This again raises the question as to whether or not Harvey ever 

 noted insufficiency or stenosis of the valves in humans. He is speak- 

 ing as an comparative anatomist here. 



According to Galen (J. C. Dalton, Doctrines of the Circulation^ 

 Phila., 1884, p. 250), Erasistratus named the right auriculo-ventri- 

 cular valves "tricuspids" (Tpt7XaJxt''as), and also called the valves 

 at the openings of the pulmonary artery and aorta "sigmoid" in 

 shape. Since the old Greek sigma had the form of the letter C, this 

 gave a correct impression of their semilunar form. Vesalius, in his 

 immortal De Hiimani Corporis Fabrica, Basle, 1543, p. 592, first likens 

 the left auriculo-ventricular valves to a bishop's miter. 



[ 121 j 



