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Show 144 MR. F. E. BEDDARD ON THE [Mar. 18, by its insertion on to the valve the junction between its fleshy and membranous portions ; on the right side the valve is muscular, on the left it is membranous. If this comparison be just, it seems to follow that the septal portion of the light auriculo-ventricular valve is not entirely wanting in the Bird's heart, as it has been generally stated to bel. In view of the possible comparison between that part of the Bird's valve which lies to the right of the fleshy bridge (when the heart is placed on its left side with the apex downwards) and the membranous or "septal" flap, as it has been better termed by Lankester ", of the Crocodile's heart, it is important to bear in mind the following fact, that this part of the valve in the Birds heart, though sometimes as thick and fleshy as the rest, is often thin and delicate and sometimes partially membranous. Furthermore, the trabecular uniting the valve with the parietes have not entirely disappeared from the Bird's heart. Gegenbaur himself implies that they have by the quotation on p. 143. But iu many birds, for example in the heart of Burmeister's Cariama (Chunga bur-meisteri) shown in the accompanying drawing (woodcut fig. 2), the margin of the valve is tied down to the free ventricular wall by several delicate muscular or tendinous threads in addition to the large fleshy bridge, which is a constant structure in the bird's heart. Next, as to the partial persistence of the septal flap in the Condor's heart. In one specimen which 1 dissected some years ago, I observed no traces whatever which could be compared to a septal flap. In the specimen which is more particularly described in the present paper there were a series of tiny yellowish spots and vesicles a little way from the posterior margin of the atrio-ventricular orifice, which formed a line occupying a position identical with that wdiich would be occupied by a septal part of the valve if it were present. The structures in question seem to me to be probably pathological; but it is a significant fact that they are situated along a line which would correspond to the insertion of a septal half of the valve ; I can, indeed, quite believe that in many Condor hearts a thickening such as that described by Gegenbaur exists, which is possibly, as a rudimentary structure, especially prone to disease. In Chung a burmeisteri (see woodcut fig. 2) a baud of muscles connects the fixed and free wall of the right ventricle ; from this are given off several threads connected with the supplementary muscular bands which tie down the edge of the valve to the free wall of the ventricle. This muscular pillar is, 1 presume, the equivalent of the moderator band in the heart of Casuarius described by Prof. Rolleston. It has been, I think, suggested somewhere that this moderator band is the equivalent of part of the septal portion of the 1 Owen (article " Aves," Todd's ' Cyclopaedia of Anatomy,' vol. i. p. 331) has erroneously compared, as Gegenbaur pointed out, this fleshy bridge of the Bird's heart with the entire membranous part of the valve in the Crocodile's heart. I find that Sabatier has apparently made the same comparison as that urged iu the text. - " O n the Eight Cardinal Valve of Echidna and of Ornithorhynchus," P. Z. S. 1883, p. 831 et seq. pi. iii. fig. 1, 3, 4, pi. iv. figs. 5, 6. |
