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Show 1903.] ANATOMY OF THE JAPANESE SALAMANDER. 305 no fenestra?-at least visible fenestra?. This flap appears to be purely membranous. Anteriorly it is continuous with the rest of the interauricular septum, which, on the contrary, is entirely muscular. It is much fenestrated, and consists below of vertical pillars passing from the dorsal to the ventral wall of the auricle. There is also, particularly on the side adjoining the fibrous part of the septum, a mesh-like disposition of the muscular strands such as Huxley has figured in Menobranchus*. The completeness of the separation of two auricles, not indicated externally, I may repeat, is furthermore shown by the fact that they debouch quite independently of each other into the ventricle. The septum between the two auricles is almost suggestive of a heart-valve in being partly muscular and partly membranous. And it may possibly be the case that the septum is physiologically something more than a mere partition-wall-and incomplete at that-between two neighbouring cavities. It may possibly by its own Text-fig. 30. Auricular septum of Megalobatrachus, viewed from in front. The membranous part is dotted. contraction, by the contractions of the muscular part playing upon the tendinous sheet, do something to stop or facilitate at different periods of the heart's beat the admixture of arterial and venous blood before it reaches the ventricle. I greatly regret that, having only one large heart at m y disposal, I a m unable to push this matter any further. I do not find myself absolutely in accord with the account of the interauricular septum given by Hyrtl or with his figure of the same. Hyrtl describes the septum as extremely delicate but imperforate, and as arching over the atrio-ventricular orifice. It is clear that this is only that part of the septum which I have described as thin and imperforate. Hyrtl does not refer to the muscular pillars which tie down the rest of the thin, and in parts * Loc. cit. pi. 32. fig. 5. PROC. ZOOL. Soc-1903, V O L II. No. XX. 20 |