OCR Text |
Show 12 DR. J. MURIE ON CYGNUS BUCCINATOR. [Jan. 10, rings I shall mention hereafter, but here only point out they are like Yarrell's plate, and not Hincks's figure of them in his C. buccinator. The second figure (fig. 2) represents the sternum of the skeleton in the British Museum, contrasted with that of its companion bird (fig. 1), The disposition and inflexions of the trachea correspond to the one first described, and with it confirm the accuracy of Yarrell's distinctions between the Hooper, with one vertical sternotracheal convolution, Bewick's Swan, with a single horizontal one, and the Trumpeter with two, one in each of these directions. In the specimen in question (fig. 2) the posterior tracheal osseous eminence is situated nearly equidistant between the right and left sides. Its length is not so sharply defined as in the other ; but its measurements correspond to about 3 inches long and 1| broad. Neither is it so lop-sided in form, and it wants the posterior truncation present in its fellow bird, while its surface rises from each margin equally, until attaining in the middle a height of \ an inch above the level of the horizontal sternal plate. There is a very slight foramen or deficiency of bone towards the left side. The anterior tracheal bony prominence is ovoid, and not heart-shaped as in the College specimen. The depression or shelf upon which the end of the trachea and bronchia? rest is not so broad nor by any means so scooped out as in the other. The greatest height which the bone reaches in this cavity is but 1\ inch, and the-sides are less perpendicular. The sterno-tracheal elevations in the points mentioned above, particularly the height of the anterior and less magnitude of the posterior, agree closely with those of C. passmori. The posterior sternal emarginations in the British Museum specimen are both uncovered, and neither of them is so deep or smooth-edged as in the companion bird. The greatest length of the sternum is 8|, and its breadth behind 3| inches. The costal edges run almost parallel; the terminal manubrial and ensiform plates are comparatively the narrowest; and the sternum altogether is shallower inside, or at least shelves more gradually towards the middle. Over and above these strictly sternal differences, the rings of the trachea in the two birds present variation. In the British Museum specimen the bony rings, from the bend of the neck to where the trachea enters the keel, are intermittingly broad and narrowed or wedge-shaped on the upper a.id lower halves; in other words, each half of the ring is unequal in breadth and dovetailed to those on either side of it, just as Hincks has depicted (loc. cit. p. 6. f. 8) in the trachea of his C. buccinator, where it divaricates at the bronchia?. In the College specimen the rings are nearly uniform in breadth or very sparingly show this peculiar kind of wedge-shape. In both specimens the trachea, after its emergence from the sternum has wider, regular rings, such as Yarrell's sectional view illustrates • but the College specimen has here and there a tendency to revert to the unequal form. |