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Show 1882.] OF ORNITHORHYNCHUS PARADOXUS. 559 Fig. 9. Right auriculo-ventricular valve of Phalangista. a, b, anterior musculi papillares. 10. Ditto of Phascolomys. Letters as before. 11. Ditto of Mus. Letters as before. PLATE XL. Fig. 12. ORNITHORHYNCHUS No. 1. Right ventricle opened and its anterior wall reflected so as to expose the valve. a, great or anterior muscular column (musculus papillaris); b, right muscular column (musculus papillaris); e, left or " conus" muscular column; P. A, orifice of pulmonary artery; E. A, right auricle; E. V. C. 8, right vena cava superior; A, aorta. 13. O R N I T H O R H Y N C H U S N O . 2. Similar dissection of a second specimen. a, great or anterior muscular column; b, b, b, the three slips which represent the single column b of specimen No. 1 ; m, n, two additional muscular columns in the same region, which do not traverse the membranous part of the valve, but pass from the centre of the right muscular arch to the anterior wall of the ventricle, from connexion with which they have been cut, leaving the bases m',n'; x,y, " columnse carnese " connecting the base of the great muscular column with the anterior ventricular wall; x', y', the cut bases of the same; e, left muscular column; P. A, orifice of pulmonary artery. 14. O R N I T H O R H Y N C H U S N O . 1. The great anterior column cut and the valve reflected. Letters as in fig. 12. 15. O R N I T H O R H Y N C H U S No. 1. Both the great'and the right muscular columns are cut. Compare with the human heart, fig. 2. Letters as in fig. 12, except lac, left anterior portion of the membrane of the valve ; r a c, right anterior portion of ditto; p c, posterior or septal portion of ditto. 16. ORNITIIORIIYNCIIUSNO. 2. The second heart (that of fig. 13) with its muscular columns cut and the valve reflected. a, base of the great muscular column; a', its cut and reflected ostial portion ; b, b, bases of two of the right small muscular columns ; b', b', their cut ostial portions; e, left muscular column; lac, left anterior portion of the membrane of the valve ; rac right anterior portion of ditto; p c, the very minute posterior or septal rudiment of ditto. 17. View of the left auriculo-ventricular valve of Ornithorhynchus. The apex of the ventricle has been cut away ; and the observer is supposed to look upwards towards the aortic and auricular orifices, eb d, three muscular columns (papillary muscles) giving attachment to the valve; cor, corpuscles resembling the corpuscula Arantii, at the central point of the margin of each flap of the triradiate valve ; L. A, left auricle ; Ao, aortic orifice. PLATE XLI. Fig 18. Right auriculo-ventricular valve oi Bidelphys. a, equivalent of the great anterior papillary muscle of M a n ; b, equivalents of the right anterior papillary muscle of Man. 19. Ditto of Phascolarctos. 20. Ditto of Myrmecophaga. e, as in fig. 1. 21. Ditto of Erinaceus. 22. Ditto of Cuscus. |