OCR Text |
Show 1867.] DU. J. MURIE ON CYGNUS BUCCINATOR. 1 1 now in the College. The trachea in it, as Yarrell (loc. cit.) has described and most beautifully figured in a profile section of C. buccinator, comes down the neck, enters the keel, runs backwards to near the posterior end of the sternum, loops round and returns, entering the second highly raised hollow protuberance on the dorsum, again dipping ere it makes its exit under the furcula. So far this all agrees with what Prof. Hincks says of C. passmori ; but this author lays stress on the shape and size of the bony expansions lodging the bent trachea, and describes afresh the structure in what he believes to be the true C. buccinator. The College specimen has the posterior osseous expansion 3*1 inches long, and 1*2 broad at its greatest diameter. This expansion is of an oval shape, rather truncated behind, and placed very much to the left side of the median line, excentric in this particular. Its right side is lowest; at *6 inch from that edge, and almost at what corresponds to the middle of this part of the sternum, is a slightly depressed longitudinal furrow ; from this to the left margin the bony expansion rises more quickly, until attaining a maximum height of Y^ of an inch above the horizontal sternal plate; the left edge is nearly perpendicular. Between the anterior end of the posterior and the posterior end of the anterior osseous protuberance, the superficial protecting lamina of bone is wanting, here exposing the trachea. The anterior, smaller but much more elevated hollow is somewhat heart-shaped, the indented broader end forwards; but here a a narrow isthmus of bone joins it to the anterior sternal arch. On its left superficies it is somewhat low and flattened, where rests the laterally compressed termination of the trachea, before giving off the enlarged globiform bronchiae. On the right moiety the bone rises f of an inch higher, and is as it were compressed on either side, but has a high arched form when viewed in profile. The dimensions of this bony protuberance are 1*5 inch from before backwards, and fully 1 inch in its greatest transverse diameter. It is raised a little more than an inch above the highest level of the outer sternal plate of bone, to which the foremost ribs are attached. The two posterior sternal emarginations are finger-shaped, and above an inch deep. The left one is overlapped and partially hidden by the after tracheal protuberance (see fig. 1). The greatest length of the entire sternum is 8^ inches ; the extreme breadth, viz. posteriorly, equal to 4 inches. The side view agrees in the main with Yarrell's figure ; Hincks's does not display the details of structure so accurately. Looked on from above or inside, as in the figure (fig. J), the two costal edges have a long but shallow concave outline, so as to produce a tendency to a sand-glass form. In the total length of the sternum and in the height and inclination to the right of the anterior protuberance it thus corresponds to Hincks's description of his C. buccinator ; but the breadth agrees with O. passmori and with Yarrell's C. buccinator. The tracheal |