10 PROF. E. R. LANKESTER ON THE CARDIAC [Jan. 16, 



No trace ot a septal membranous valve-flap exists in this heart. 



It is a noteworthy fact, in view of the statement which has been 

 made by Gegenbaur as to the existence of a septal portion to the 

 right cardiac valve of Ornithorhynchiis, that, in the nine specimens 

 examined by me, only two. No. 1 (of my former paper) and Dr. Pye 

 Smith's specimen, have any thing entitled to be called a septal flap ; 

 and in both these cases it is exceedingly small, fringing one third 

 onl}' or less of the septal margin of the auriculo-ventricular ostium. 



In seven of the hearts examined a septal portion of the valve was 

 not present. 



Comparison with the Right Cardiac Valve of Casuarius and Croco- 

 dilus. — I have introduced, in the Plates illustrating this note, drawings 

 (carefully prepared from dissections in my possession) showing the 

 right cardiac valve of the Cassowary (Plate III. figs. 5, 6) and the 

 corresponding structure of the Crocodile (Plate IV. figs. 1, 2). 



Both are prominently distinguished from the corresponding struc- 

 ture in Ornithorhynchus by having the anterior flap of the valve 

 entirely muscular ; no membranous area is present in that flap, either 

 in Cassowary or Crocodile. 



The Crocodile's right cardiac valve consists of two nearly equally 

 large flaps or lobes, an anterior (Plate IV. figs. 1, 2, a) and a septal 

 ipp)- The anterior portion of this valve is comparable with the 

 fleshy masses h b and a of the Ornithorhynchus-he&xt drawn in Plate 

 III. fig. 1 ; but there is absolutely nothing in the heart of Ornitho- 

 rhynchus which has any relation to the septal flap, p^, of the Croco- 

 dile's heart, excepting the rudiment mentioned above as found in 

 only two hearts out of nine. The septal flap in the Crocodile is 

 larger than the anterior muscular flap, and is almost entirely mem- 

 branous. Its septal face, however, is invaded to a certain extent by 

 small muscular bands. 



I cannot consider that Gegenbaur is correct in indicating a cor- 

 respondence between the structure of the right cardiac valve in Orni- 

 thorhynchus and Crocodilus closer than that which obtains between 

 the Monotreme and other Sauropsida with fleshy right cardiac valve. 



On the other hand, in the bird's right cardiac valve, Plate III. 

 figs. .5 and 6, we find no septal lolie (either membranous or mus- 

 cular) to vitiate the comparison with that of Ornithorhynchus ; and 

 I must maintain that Prof. Owen was more correct in pointing out 

 resemblances between the right cardiac valve of Ornithorhynchus 

 and that of birds than Gegenbaur has been in assimilating the former 

 to the corresponding structure in Crocodiles. The agreement, such 

 as it is, by no means tends necessarily to indicate any special mor- 

 phological relationship between Ornithorhynchus and birds, which 

 have been conclusively shown by Huxley and by Gegenbaur to have 

 no nearer genealogical meeting-point than in the forefathers of the 

 common ancestor of Sauropsida. 



The specialization and separation from the ventricular v/all of the 

 muscular slip e in the Cassowary's heart is a marked modification of 

 a part which can be traced in the mammalian heart (see former paper 

 pi. xl. e). The fact that in the bird the muscular substance of the 



