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Show 1883.] VALVES IN ECHIDNA AND ORNITHORHYNCHUS. 11 large mass a b runs upwards to the auricular ostium from the outer free ventricular wall rather than from the ventricular septum, as in Ornithorhynchus and other Mammals, appears to me to have very little importance. The moulding of the ventricular cavities may very readily result in an apparent dislocation of parts, so as to give the muscular upgrowths of the ventricular wall at one time a septal, at another time a free-wall attachment. This variation is seen in higher mammalian hearts, as for instance in the Seal (Phoca vitulina), where important musculi papillares are attached, not (as is usual) to the septal, but to the free ventricular wall. Lumen of the Right Ventricle in Ornithorhynchus.-In figs. 3 and 4 of Plate IV. sections are represented taken across the ventricles of the heart of Ornithorhynchus and Lepus. The drawings are intended to show the Sauropsidan character of the heart of Ornithorhynchus, in that its right ventricle appears thus in section as a crescentic sac embracing the very thick-walled cylindrical left ventricle, as in Birds and Reptiles, whilst in the normal Mammalia as represented by Lepus the right ventricle does not embrace the left ventricle so closely, and presents, instead of a strongly convex septal wall, a nearly plane one. Right Cardiac Valve of Echidna hystrix.-I am not acquainted with any figure of the right cardiac valve of the second genus of Monotreme Mammalia, Echidna. Prof. Owen, in vol. iii. of his 'Anatomy of Vertebrates,' p. 517, thus describes it:-" The tricuspid valve is membranous and consists of one principal portion closing the outer angle ; the free margin of the valve is attached to the extremity of a large fleshy column arising by different roots from both the fixed and the free walls of tbe ventricle ; a short fleshy column is attached to the left extremity of the valve ; some chordse tendineae are fixed to its right angle." The membranous character of the valve and "the large fleshy column (a) arising by different roots (x and y) " will be recognized in the drawings on Plate IV. figs. 5, 6, 7. I am not able any further to identify in the hearts kindly placed at my disposal by Professor Flower the other features mentioned by Professor Owen. As compared with the hearts of Ornithorhynchus already described, the two Echidna-hearts present one important difference. The membranous substance of the valve is not traversed by the muscular columns or musculi papillares connected with it. These muscular columns are simply inserted into or fixed to the membrane, and do not, as in Ornithorhynchus, pass upwards through it so as to be inserted into the auriculo-ventricular ring. Membrane alone depends from that ring, as in the Marsupial and Placental Mammalia. At the same time an equally important agreement with Ornithorhynchus and difference from other Mammalia is presented by Echidna in a leading feature of the construction of its right cardiac valve. This feature is the total absence (in the two specimens studied by me) of a septal flap. This character is clearly exhibited in the three dissections drawn in Plate IV. figs. 5, 6, 7. The muscular columns (musculi papillares) agree pretty closely with those of some Ornithorhynchus-hearts in number and origin |