190 



DR D. NOEL PATON ON THE 



contract along with the rest of the ventricular wall, and close the valves as above 

 described. 



It may be asked, " If this is the mode of action of the tricuspid valve, what is the 

 meaning of the small internal cusp ? " Possibly, with a small amount of blood behind it, 

 it may act as a cushion against which the external cusps may rest. It is, however, more 

 probably simply to be regarded as a developmental remnant of the " Ohrkanal " described 

 by His, from the walls of which the auriculo- ventricular valves are developed. 



Many of the older physiologists have fully appreciated the difficulties in the acceptance 

 of the commonly taught theory, and, from a consideration of the anatomy of the heart, 

 have been led to advocate the view, the correctness of which, I believe, I have succeeded 

 in demonstrating. 



Meckel (Handbuch der menschlichen Anatomie, Bd. iii. S. 23, 1817) appears to 

 have been the first to suggest that the valves were closed as above described. 



After describing the papillary muscles, he says,' — " Indem diese sich bei den 

 Zusammenziehungen des Herzens verktirzen, werden die verschiednen Abschnitte der 

 Klaj)pen in die Hohle des Herzens einander gegen gezogen, und so die Mundung 

 kraftig geschlossen. " 



Mayo, in 1829, gave a very clear description of the action of the valves. The 

 following is taken from his Outlines of Physiology, 4th edition, 1837, p. 42. 



" The action of these fleshy columns, and of the tendinous cords in closing the valve, 

 may be easily understood from the adjoining figures. 



" Fig. 1 represents the mitral valve during the diastole of the ventricle, the fleshy 



columns relaxed, the chorda? tendinese loose, the passage 

 through the auricular valve patulous. 



" Fig. 2 represents the condition of the valve during the 

 ventricular systole : its edges are then drawn into contact, so 

 as to form a kind of flattened conical projection into the 

 ventricle." 



He considers that the action of the tricuspid valve takes 

 place on the same principle as that of the mitral, and that it 

 is never properly closed. 



Eeid, in his article on the heart in Todd's Cyclopedia of 

 Anatomy and Physiology, 1836, says, "That the lips of the 

 valves are approximated in this manner " (described by Mayo) " appears to me to be the 

 much more probable opinion." 



Hope (Diseases of the Heart, 1839) gives a very similar description of the action of 

 the valves, and states that the credit of originating the theory belongs to Mayo. 



Burdach (Traite de Physiologic, traduit de VAllcmand sur la deuxieme edition, par 

 A. J. L. Jourdon, 1827, t. vi. p. 239) develops precisely the same theory. 



In an admirable treatise, " Du Cceur, de sa structure et de ses mouvements, ou Traite 



