182 DR D. NOEL PATON ON THE 



auricles. This was probably due to the fact that the papillary muscles were not 

 directly stimulated, and that therefore the closure of the valves was not complete. Indeed, 

 on account of the indirect stimulation of the papillary muscles as compared with the 

 ventricular wall, this method would specially favour the assumption of a horizontal posi- 

 tion of the cusps of the valves. 



To fix the heart in diastole the vessels were ligatured, arid the organ was suspended 

 in water until rigor-mortis had passed off, and was then hardened first in Muller's solution 

 and then in alcohol. 



With dogs and cats the animal was killed with chloroform, and the heart rapidly 

 excised and treated as above described. 



For the human hearts I have examined, I have to thank Dr Barrett, who was good 

 enough to let me have a number of unopened hearts from the post-mortem room of the 

 Royal Infirmary. Most of these were lax, post-mortem rigidity having passed off". By 

 removing the clots, filling the cavities with spirit and hardening, one was able by making 

 sections to study the relationship of parts in diastole. Some specimens were obtained in 

 the condition of rigor-mortis, and these, after hardening in spirit, showed to some extent 

 the relationship of parts in the third stage of ventricular systole. But inasmuch as 

 the factor of blood-pressure had not had full play, the valves were never found in quite 

 the same position as in the heart prepared as described above. 



I am also indebted to Dr Gibson for a number of specimens of hearts from young 

 subjects, which had been hardened in the condition of more or less firm rigor-mortis, and 

 from which some of the figures were prepared. 



Sections were made in different planes, but chiefly in those indicated in fig. 4. The 

 sections were photographed, either before or after removal of the coagulated blood, and 

 then preserved in spirit. 



In this way a very complete picture was obtained of the position of the valves during 

 the various phases of the cardiac cycle, while the mechanism by which the various 

 changes are produced was also rendered clear. 



Anatomical Considerations. 



It will be necessary, in the first place, merely to allude to certain points in regard to 

 the position of the orifices, valves, papillary muscles, and chordae tendinese. Although 

 these matters are dealt with in anatomical works, the descriptions given are far from 

 complete or satisfactory. 



The chordae tendinese are not, as is usually described, entirely inserted into the margins 

 and ventricular surfaces of the valves, but are to a large extent continued upwards along 

 the surface of the valves, to be inserted into the auriculo-ventricular rings (fig. 6). Dr 

 Symington has shown me a specimen in which the muscular fibres of the papillary muscle 

 are continued upwards and inserted into the auriculo-ventricular ring. When the papil- 



