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Show 10 PROP. E. R. LANKESTER ON THE CARDIAC [Jan. 16, No trace of 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 Ornithorhynchus, that, in the nine specimens examined by me, only two, No. 1 (of m y 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 only or less of the septal margin of the auriculo-ventricular ostium. In seven of tbe hearts examined a septal portion of the valve was not present. Comparison with the Right Cardiac Valve of Casuarius and Crocodilus.- I have introduced, in the Plates illustrating this note, drawings (carefully prepared from dissections in m y 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 structure 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 (pp). The anterior portion of this valve is comparable with the fleshy masses bb and a of the Ornithorhynchus-he&vt drawn in Plate III. fig. 1 ; but there is absolutely nothing in the heart of Ornithorhynchus which has any relation to the septal flap, pp, of the Crocodile'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 membranous. Its septal face, however, is invaded to a certain extent by small muscular bands. I cannot consider that Gegenbaur is correct in indicating a correspondence between the structure of the right cardiac valve in Ornithorhynchus 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 lobe (either membranous or muscular) to vitiate tbe 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 morphological 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 wall of the muscular slip e in the Cassowary's heart is a marked modification of a part which can be traced in tbe mammalian heart (see former paper pi. xl. e). The fact that in the bird the muscular substance of the |