OCR Text |
Show l^Q.] TRACHEA OF THE GALLINiE. 355 that anteriorly it is slightly bent downwards in the middle line, assist m the changes of form connected with the bifurcation of the tube. The penultimate ring, from its position, is more pronounced in this respect, whilst posteriorly the pessulus runs up to blend with it, not at its inferior margin, but by a wedge-shaped cartilaginous expansion, the apex of which touches the lower margin of the ring above. That this is so is proved by the existence of two oblique indented lines, one on each side, converging superiorly, where they nearly meet to form the apex of the just-mentioned wedge. The last tracheal ring anteriorly sends down an obtuse median process, the inferior margin of which constitutes the summit of the notch Fig. I. Fig. 2. Front view. Back view. Pavo spicifer (adult). N.E.-This and all the subsequent diagrams are drawn to one scale, and have no relation to the actual size of the structures. between the divaricating bronchi, whilst its posterior surface forms the anterior attachment of the pessulus. Posteriorly this ring is incomplete, the tw7o obliquely truncated ends being separated by a considerable interval occupied by the pessulus in the middle line, and laterally by the commencement of the membranous inner walls of the bronchi. In the middle of the upper border of the penultimate ring anteriorly a white line is seen sending a limb down on either side, beyond the ring itself, onto the next, at the lower margin of which it ceases at the root of the obtuse median process. Such an appearance indicates that in the older bird fusion of the two rings will occur at the spot, as an inspection of the part in the adult verifies. From the above description it will be also seen that the pessulus- a slender cylindroid bar, expanded and flattened at each end-is anteriorly attached to the last, and posteriorly to the penultimate 23* |