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Show 188 MR. F. E. BEDDARD ON THE HEART OF APTERYX. [Feb. 17, 2. On the Heart of Apteryx. By F. E. BEDDARD, M.A., F.R.S.E., Prosector to the Society. [Eeceived February 17, 1885.] The structure of the heart of Apteryx has been described somewhat fully by Sir Richard Owen in his well-known memoir upon the anatomy of the Southern Apteryx ] ; this account is illustrated by two figures, one of which represents the heart in its entirety viewed from the right side, while the other is a view of the same region of the heart, with the wall of the right ventricle removed in order to display the structure of the right auriculo-ventricular valve. The description given of the right auriculo-ventricular valve is as follows :- " T h e principal deviation from the ornithic type of the structure of the heart is represented in the valve at the entry into the right ventricle (pi. Iii. fig. 3 ). This is characterized in birds by its muscularity and its free semilunar margin. In the Apteryx it is relatively thinner and in some parts semitransparent and nearly membranous ; a process moreover extends from the middle of its free margin, which process is attached by two or three short chorda tendinea to the angle between the free and fixed parietes of the ventricle. W e perceive in this mode of connection an approach in the present bird to the mammalian type of structure analogous to that which the Ornithorhynchus, among Mammalia, offers, in the structure of the same part, to the class of birds ; for the right auriculo-ventricular valve in the Ornithorhynchus is partly fleshy and partly membranous." The figure which illustrates this description is entirely in harmony with it, but does not at all represent the structures observable in the hearts of Apteryx that I have myself studied. In a heart of Apteryx austra/is, which I found among the Prosector's stores, the right-auriculo-ventricular valve is composed of two halves which unite together at a point nearly opposite the auriculo-ventricular aperture, and are connected there by a muscular flap to the dorsal (free) wall of the ventricle. The right half is the larger and arises chiefly from the free wall of the ventricle, partly, however, from the septum and from the point of union of the septum with the free wall; it is of uniform thickness and muscular throughout. The left half of the valve is considerably smaller; it arises from the inter-ventricular septum and from the septum between the ventricle and the auricle ; like the right valve, it is muscular throughout with the exception of a very minute membranous portion lying at the lower side of the valve; this portion of the auriculo-ventricular valve is not of uniform appearance like the left, but is formed 1 Trans. Zool. Soc. vol. ii. p. '212. |