I 



THE HARVEIAN ORATIOIT. 74i^ 



Every gradation, in fact, exists between the entire obsolescence 

 of the moderator band, which we sometimes see in the human 

 heart, through the typical, and I should anticipate, constant, but 

 not functionally important, representation of it in the rabbit, up to 

 the important and structurally prominent development attained to by 

 it in the ungulate mammal, and this solitary instance for the class of 

 birds, and the sub-class, with such generalised affinities, of struthiones. 



And, speaking of the method of gradations, I take this opportu- 

 nity of saying that its application in the case of the muscular right 

 auriculo-ventricular valve of birds will, in my judgment, put an 

 end to the disputes which have taken place as to its homology with 

 one or other of the two valves in the crocodiles. The two portions 

 of the valve in the Castiarms austraUs are so nearly equal — the 

 larger being 1-7 inch, as against i'4 of the smaller-^as to do away 

 with the difficulty which might be felt in holding that both croco- 

 dilian valves are represented here. There are other reasons for thjs 

 view, which I reserve for another occasion. But whilst speaking of 

 the heart of the bird, I cannot forbear pointing out how the struc- 

 tural arrangements of its auricle^ differing as they do strikingly 

 from those of the same compartment in the mammalian heart, help 

 us by that contrast to get a true idea of the working of this latter. 

 Firstly, the walls of the bird's right auricle are relatively thicker, 

 not only as compared with the walls of its own ventricle, but also 

 as compared with the walls of the corresponding auricle in the 

 mammal, the musculi pectinati standing out in as sharp relief as 

 the similarly working muscular ridges in a hypertrophied bladder, 

 and inclosing anfractuosities and recesses almost as deep. But, 

 secondly, and what is of more importance, the bird's auricle is 

 furnished with a large and functionally active valve, protecting the 

 entrance of the great veins, and preventing regurgitation into 

 those vessels just as the auriculo-ventricular valves prevent regur- 

 gitation from the ventricles. It is fair to argue a priori that if the 



what I would call the 'eowaf?' and ' dextrad'' cusps of the tricuspid, to an origin oh 

 the interventricular septum, sending a root up to the point of origin of one of the 

 chordae tendineae of the third cusp, called ' septal ' by Mr. Galton. See also Mr. 

 Galton's Letter to 'British Medical Journal,' July 26, 1873, p. 83. I have to thank 

 Dr. Headlam Greenhow for a reference to another notice of the presence of a 

 moderator band in a human heart. It will be found in an interesting paper of his in 

 the 'Transactions of the Pathological Society,' vol. xxi. 1870, p. 88. 



[It should be stated that Mr. T. W. King had figured and described a moderator 

 band in the human heart and in several mammals other than the Ungulates. — Editor.] 



